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OnBoard Diagnostic II (OBD II) HELP

Real information you can use to diagnose your car or truck

Copyright AA1Car.com

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The Malfunction Indicator Lamp (MIL) or CHECK ENGINE light as it is more commonly called, is essentially an emission warning light. If the light comes on, it means the Onboard Diagnostics II system (OBD II) has detected an emissions-related problem. OBD II is designed to turn on the MIL light if a problem occurs that may cause emissions to exceed federal limits by 150 percent. The problem has to occur more than once, and it must be significant enough to create a potential emissions problem (one serious enough to prevent a vehicle from passing an emissions test).

In the real world, the MIL lamp often comes on for what seems like trivia reasons (like a loose gas cap). But there's no way to know what's triggering the light until the vehicle is diagnosed. The problem may be something minor that has little or no effect on driveability, or it may be something more serious that is affecting engine performance.

The mysterious nature of the MIL lamp, which most people call the "Check Engine" light, terrifies and confuses a lot of motorists. Except for a few luxury vehicles that actually display a fault message when the MIL lamp comes on, most

provide no information whatsoever other than something is wrong. The motorist has no way of knowing if the problem is major or minor -- or what it will ultimately cost to have the problem diagnosed and repaired.

Some motorists, on the other hand, seem unfazed by warming lights. As long as their vehicle continues to run, they see no urgency to have their engine checked, to slow down or to do anything out of the ordinary. Others are optimists and hope that if they keep on driving, the light will magically go out. Sometimes it does, much to their relief. But when the light refuses to go out, or it comes and goes like the ups and downs of the stock market, they panic and don't know what to do.

Some motorists who are befuddled by a Check Engine light will seek out the least painful (and cheapest) solution which is to take their vehicle to an auto parts store that offers a "free diagnosis." The diagnosis consists of plugging in a code reader into the DCL connector and reading out the code. The auto parts stores who offer a free diagnosis service say the code will usually reveal the nature of the problem so the motorist can decide what to do next. They're hoping, of course, that the motorist will buy a part from their store and install it themselves to fix their problem. And if that doesn't work, that the motorist will buy another part and install that in hopes it will solve the problem. And when that doesn't work, that the motorist will buy yet another part and install it themselves in hopes of fixing he problem. You get the picture.

Anyone who repairs late model vehicles today for a living knows that diagnosing complex emissions and driveability problems is not as simple as reading a code and replacing a part. OBD II is a great system that has a tremendous amount of self-diagnostic capability, but it only identifies faults in particular circuits or systems. It does not tell you which component to replace. That can only be determined after doing additional diagnostic work to isolate the fault.

Some problems such as misfires and evaporative emission (EVAP) leaks can be very challenging to nail down. Misfires can be caused by ignition problems, fuel problems or compression problems. The underlying cause might be fouled spark plugs, bad plug wires, a weak ignition coil, dirty injectors, a shorted or open injector, low fuel pressure, a vacuum leak, a leaky head gasket, burned exhaust valve or a camshaft with a bad lobe. No simple plug-in diagnosis will give you the answer until you do a lot of other checks.

To make matters worse, some of these friendly auto parts stores will also erase the code(s) after they've given their customer the diagnosis. Erasing the code turns out the MIL light -- at least temporarily -- which provides some relief for the poor motorist. But it may also make the job of diagnosing the fault harder if valuable diagnostic information that you might have needed was erased.

OBD II & EMISSIONS TESTING

Another diagnostic issue that's becoming more of an issue with OBD II is that a growing list of states are now substituting an OBD II emissions test for a tailpipe test. The OBD II test is quick and easy, goes not require an expensive dyno or emissions analyzer, and gives a pass/fail indication in a minute or less. There's no risk of damage to the vehicle (as may be the case when running a vehicle on a dyno), and the reliability of the OBD II test is actually better than a tailpipe emissions test. Why? Because the OBD II system monitors emissions 24/7 365 days a year. There are no arbitrary cutpoints that can be fudged one way or the other to pass or fail more or less vehicles. Everybody dances to the same tune and must meet the same standards.

OBD II is also much better at detecting evaporative emissions leaks, and a drop off in converter efficiency. If the MIL light is on and there's a code for an EVAP or converter problem, you can usually bet the problem is real. The problem may not have any noticeable effect on driveability or performance, but technically it is in violation of the standards -- and must be fixed before the MIL light will go out and say out.

OBD II monitors evaporative emissions by checking for fuel vapor leaks once a drive cycle. OBD II does this by applying vacuum or pressure to the fuel tank, vapor lines and charcoal canister. If it detects no airflow when the EVAP canister purge valve is opened, or it detects a leakage rate that is greater than that which would pass through a hole 0.040 inches in diameter (0.020 inches for 2000 and up model year vehicles), it indicates a fault.

If you find a P0440 code that indicates a fuel vapor leak, finding the leak can be a challenge. The first place to start is the gas cap. A loose-fitting or damaged cap can allow enough air leakage to set a code. To find a leak in a vapor hose, you may need a leak detector that uses smoke and/or dye. A 0.020 inch hole is the size of a pin.

PLUG-IN DIAGNOSTICS

All OBD II-equipped vehicles have a common J1962 16-pin diagnostic connector and use the same "generic" fault codes. This means all you need is an OBD II-compliant code reader or scan tool to check readiness status, and to read and clear codes. The state emission programs require vehicle inspection facilities to use a more sophisticated plug-in tool that also records vehicle data for record keeping purposes, but otherwise they are using the same basic scan tool technology as everybody else.

To access the OBD II system all you have to do is plug a code reader or scan tool into the 16-pin connector (note: there are no "manual flash codes" on OBD II systems). The connector is usually located under the dash near the steering column. But on some vehicles, it can be hard to find. On many Hondas, the plug is located behind the ashtray. On BMW and VW, it is behind trim panels. On Volvo, the plug is next to the hand brake. On Audi, you'll find it hidden behind the rear seat ashtray.

THE OBD II PLUG-IN TEST

An OBD II test is a simple plug-in computer check that verifies four things:

1. The Vehicle Identification Number (VIN). 2. That the vehicle's OBD II system is ready (all required readiness monitors have been set). 3. The status of the MIL lamp. The lamp must be functioning correctly and come on when commanded to do so. Otherwise, it must be off indicating no codes. 4. That the vehicle has no diagnostic trouble codes that would cause the MIL lamp to come on.

OBD II monitors misfires, converter efficiency, catalyst heater (if used), the evaporative system, air injection system (if used), fuel trim, oxygen sensors, exhaust gas recirculation (if used), secondary air system (if used), the coolant thermostat (starting in 2000), positive crankcase ventilation system (starting in 2002) and even the A/C systems on some 2002 and newer vehicles.

If a situation develops in any of these monitored systems that could cause a real or potential emissions problem, OBD II will watch it, set a code and eventually illuminate the MIL. Most OBD II codes take time to mature and will not turn on the MIL lamp immediately. OBD II may wait until it detects the same problem on two separate drive cycles before it converts a pending code into a mature code and turns on the MIL lamp. The bottom line here is if the light is on, the vehicle will NOT pass an OBD II plug-in test. The problem must be fixed and the MIL light must stay out before the vehicle will pass.

READINESS ISSUES

One of the EPA's requirements for using a plug-in OBD II check in lieu of a tailpipe test is to make sure the OBD II system has run all of its monitors and that the monitors have all passed. But there's a catch. Some import vehicles have readiness issues when it comes to setting all the OBD II monitors. Consequently, the EPA currently allows up to two readiness monitors not to be set prior to testing 1996 to 2000 model year vehicles, and one readiness readiness monitor for 2001 to 2003 vehicles.

When OBD II runs a self-check on a particular component or system, it lets you know by setting a readiness "flag" or indicator which can be displayed on your code reader or scan tool. If OBD II has run all the available monitors and all the monitors have passed -- and no faults have been found -- the vehicle should pass the OBD II plug-in test. But if all the required monitors have not run, the vehicle can't be given an OBD II test. The motorist must drive the vehicle and come back again, or take a tailpipe test if that is an option.

If OBD II detects a fault when running a monitor, the setting of a code may prevent the remaining monitors from running. A bad oxygen sensor, for example, will prevent the catalyst monitor from running. Getting all the monitors to run can be tricky on some vehicles. Each monitor has certain operating requirements that must take place before the self-check will run.

To set the converter monitor, for example, the vehicle may have to be driven a certain distance at a variety of different speeds. The requirements for the various monitors can vary considerably from one vehicle manufacturer to another, so there is no "universal" drive cycle that will guarantee all the monitors will be set and ready.

As a general rule, doing some stop-and-go driving around town at speeds up to about 30 mph followed by five to seven minutes of steady 55 mph highway speed driving will usually set most or all of the monitors. Consequently, if you're checking an OBD II system and discover that one or more of the monitors have not run, it may be necessary to test drive

the vehicle to set the remaining monitors. With the EVAP monitor, the vehicle may require a certain period of inactivity (such as setting overnight) and certain ambient temperature conditions (such as above freezing) before the EVAP monitor will run.

Some vehicles with known readiness issues include 1996-98 Mitsubishi models (which require a very specific drive cycle), and 1996 Subaru and Volvo 850 Turbo (turning the key off clears all the readiness flags, so don't turn the vehicle off after driving). On 1997 Toyota Tercel and Paseo, the readiness flag for the EVAP monitor never will set, and no dealer fix is yet available. Other vehicles have often have a "not ready" condition for the EVAP and catalytic converter monitors include 1996-98 Volvo, 1996-98 Saab, and 1996-97 Nissan 2.0L 200SX.

DRIVE CYCLES

If the MIL lamp comes on while driving, or remains on after starting the engine, it means OBD II has detected a problem. The lamp will usually remain on -- unless the fault does not reoccur in three consecutive drive cycles that encounter the same operating conditions, or the fault is not detected for another 40 drive cycles. If OBD II sees no further evidence of the problem, it will turn off the MIL lamp and erase the code.

An OBD II drive cycle is not just turning the ignition key on and off or starting the engine. A drive cycle requires starting a cold engine and driving the vehicle until the engine reaches normal operating temperature. The next drive cycle doesn't begin until the engine has been shut off, allowed to cool back down and is restarted again. On some vehicles, the drive cycle also includes the cold soak time between trips. On some vehicles, the EVAP monitor won't run unless the vehicle has sit for eight hours. There no way to bypass or get around such requirements, so you have to do what ever the system requires. And if that means waiting, you have to wait.

READING DTC CODES

If OBD II has detected a fault, you should find one or more "generic" codes (which start with the prefix "P0"), and maybe one or more "enhanced" codes (OEM specific codes that start with a "P1"). All OBD II compliant code readers and scan tools should be able to display generic codes, but some do not display all the OEM enhanced codes. As a result, you may not get the full picture of what's going on if you're using a tool with limited capabilities. The same goes for accessing many OBD II diagnostic features such as history codes, snapshot data, and special diagnostic test modes that require two-way communication and special scan tool software. For example, some of the OBD II diagnostic features that are currently accessible with an OEM factory scan tool are not yet available on aftermarket scan tools. This may limit your ability to diagnose and repair certain types of problems.

An inexpensive Personal Digital Assistant (PDA) or smart phone with scanner software and cable, or even a DIY type of code reader can be used to read and clear most OBD II codes on 1996 and newer vehicles. This type of tool can often be used to make a quick diagnosis, and in many cases you don't need anything else. But for advanced diagnostics, you need a professional grade scan tool or software package with advanced capabilities.

For some jobs, you may also need a tool that can graph or display waveforms. That means buying a digital storage oscilloscope if you don't buy a high end scanner that can do both. Most scan tools display data stream values, which is what the PCM tells it to display. If the PCM is misreading a sensor input or is substituting bogus information, you have no way of knowing without actually testing the circuit or component in question. That's where a scope comes in handy.

When a scope is hooked up to a sensor or circuit, it shows what's actually going on inside that device or circuit. Voltage is displayed as a time-based waveform. Once you know how to read waveforms, you can tell good ones from bad ones. You can also compare waveforms against scan tool data to see if the numbers agree (which is a great way to identify internal PCM faults). A scope also allows you to perform and verify "action-reaction" tests. You can use one channel to monitor the action or input, and a second, third or fourth channel to watch the results. For example, you might want to watch the throttle position sensor, fuel injector waveform, crank sensor signal and ignition pattern when blipping the throttle to catch an intermittent misfire condition.

OnBoard Diagnostics II Guide

for Windows XP, Vista or 7

A Quick Reference Guide for all 1996 & newer vehicles

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Driveability Diagnostics, OBD I & II

By Steve Zack - SPX Technical Trainer and Chuck Eaves -Technical Specialist, JA Echols & Assoc Since the dawn of on-board diagnostics (OBD) in motor vehicles, the process of diagnosing driveability problems are the same as always, and very different, too. When OBD I evolved into OBD II in 1996, the electronic part of diagnosing driveability problems became a little easier. This is because the electronic network on OBD II vehicles became much more comprehensive and changed almost all mechanical functions that controlled the powertrain into electro/mechanical functions. There are three indispensable tools to diagnose OBD system problems and make the proper repairs. These tools and how to use them will be explored in some detail.

Scan Tool Diagnostics The first tool we’ll talk about is the scan tool. In general terms, there are two types of “scan tools”. One is referred to as a Code Reader. These simple electronic tools are useful and will read and erase all OBD emissions codes. Some will also give the code description, but not all code readers do this. A true scan tool, however, will read and clear OBD codes, and will do the same on “enhanced” and “sub-system” codes. These enhanced codes are OEM-specific, with OEM assigned numbers. These codes cover the entire electronic control spectrum beyond purely emissions. Beyond driveability, the codes will cover the HVAC, IPC, BCM, ABS, SRS, and electronic-bus communication systems. The true scan tool will also do many other important and useful things, and these will be discussed later. Most of you have already noted the superior functionality of the OBD II system compared to the OBD I system. Some of the enhanced capability of the OBD II system will be found on OBD I. Most, however, will not. As already mentioned, OBD II was adopted across the board in 1996. You will find a couple of models of each manufacturer that introduced OBDII as early as 1994. These early OBD II vehicles were early production models, and usually employed both the OBD II 16 pin connector and the vehicle-specific connector to access the other systems. Just remember, the scan tool reads and reports to you what the vehicle’s computer system is doing and saying. If the computer system in the vehicle can’t know or do a certain thing, like reading ignition kV, the scan tool cannot give you this information. The scan tool, then, is the interface between you and the vehicles’ computer system. There are two other tools, both of which have been around for quite a while, which are very important in diagnosing OBD problems. One is the technician; in other words, YOU. There will never come a day when the technician will not be absolutely essential to diagnose and repair OBD problems. No scan tool can fix the vehicle, and the scan tool will often only point you to the problem area. Your job is secure if you are willing to keep up with ever-advancing technology. This requires an on-going investment in education and tools. This will never change. Scan tools don’t fix cars, you do! If you do your job well, you will make a very nice living fixing everything, but nothing more, than your customer’s vehicle requires. Part of your investment in your diagnostic future is in updating your scan tool. The electronic world will never stop moving and improving. Do not get angry with your scan tool distributor for offering you the latest update when it becomes available. Out-of-date software or hardware is like having only three points on your Philips screwdriver. It will still work, sort of, for a while maybe. Don’t wait. Update your tool every chance the manufacturer gives you. You’ll appreciate the difference the first time you use your tool, especially if you’ve just updated your OTC Pegisys, Genisys, or Nemisys. The functionality improvements OTC has added to the additional diagnostic information year-to-year in the OTC family of scan tools are nothing short of remarkable.

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The third and last electronic diagnostic tool that we will address is the oscilloscope, or “scope” for short. Simply put, the purpose of a scope is to put a picture on a screen of the electrical activity that is going on in whatever you are testing. This picture is a constantly moving line trace, or graph, called a “pattern”. The scope info on the screen is “live”, not processed as with a scan tool. This fact makes scope information more accurate and more current than scan tool data, which first has to be processed by the vehicles computer, then again by the scan tool. Scan tool data is almost always reliable, but should be verified by a scope (or a digital multi-meter) before the repair is made. Otherwise, you may find yourself reading codes and pulling parts, over and over. This approach will be very unpopular with your customer, and will cost you money. A high-quality scope can be expensive, and many techs simply don’t know how to use one. The Genisys and Pegisys, by OTC , are very easy to use, full-function scan tools with a 2 or 4-channel lab/engine analyzer scope. The price is surprisingly reasonable, especially when compared to the competition. OTC’s scope module for the Genisys is a full-function 4-channel 4-color scope that accurately presents all automotive voltage from mV through kV levels. The new OTC Pegisys has an ultra-high speed 2 channel scope built in, with all the advanced capability of the Genisys’ 4 channel model, but with 2 channels for easier operation. Before beginning the in-depth discussion of how to best use your scan tool, a few basic understandings are in order. You ASE Master Techs out there, just bear with us a little bit. OBD I codes (early 1980’s through 1995) use two and three digit numbers without letters. They are all manufacturer assigned. OBD II codes (1996 up) consist of a letter followed by four numbers. There are four different letters for OBD II, and they are as follows: P – Powertrain codes, meaning engine and transmission. All emission codes start with P. B – body codes C – chassis codes U – communication-bus/network codes In the “P” code group, if the first number is “0” (zero), all the codes are “generic”. This means that any light truck and car sold in America from 1996 on share the same P0 codes. The codes mean the exact same thing on all vehicles. P1 codes, however, are OEM assigned, and mean whatever the manufacturer wants them to mean as long as they are powertrain related. The meaning of the second number in the P0 codes is as follows: 1 – Fuel metering, things like MAF, MAP, O2 sensors, etc. 2 – Fuel metering, but injector and injector circuit only 3 – Misfire and ignition 4 – Emission controls, like EVAP, EGR, CAT, etc. 5 – Vehicle and idle speed control 6 - and 7 – Transmission The last two numbers give you the specific identification within the general system. Example: P0101. This means powertrain, OBD II emissions, fuel metering, mass air flow meter. In the OBD II system, there are three types of codes. These are “Current”, “Pending”, and “History”. A current code will set the check engine light after one, two, or three “consecutive similar trips”, depending on which Monitor detects the problem. The conditions that the Monitor evaluates before deciding to illuminate the Check Engine Light are called “Enabling Criteria”. This fancy term simply refers to the process the vehicles’ computer goes through in deciding whether the problem is reoccurring and serious enough to set a code and turn on the light.

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The “check engine light” is correctly called a “MIL”, or “Malfunction Indicator Light”. We’ll call it a MIL (not MIL light). The MIL only illuminates if the problem is a P code, emissions related. All “check engine light” codes are correctly called “diagnostic trouble codes”, or “DTC’s”. Let’s just use “codes” for DTC. It’s easier. Current, Pending, and History codes (OBD II only) Many current codes will set the MIL when it comes out of Pending and into Current. If the MIL illuminates as a result of an emissions code, a History code will be recorded, and a “Freeze Frame” recording will be stored. A Freeze Frame recording saves one frame of data on several PID items such as RPM, VSS, MAP and/or MAF, IAT, ECT, etc. Accessing the Freeze Frame recording will give you an idea of just what the vehicle was doing when the MIL set. DO NOT clear your codes first. All Pending and Freeze Frame info will disappear when your code/s are cleared. If you are using the OTC Pegisys, Genisys or Nemisys, you can save the codes and Freeze Frame to tool memory before you clear your codes. The Pegisys and Genisys will automatically record a datastream list if a MIL sets while you are communicating with the vehicle. The Genisys and Nemisys recording is a staggering 1,000 frames, approximately 82 before, and 918 after the MIL illuminates, and the Pegisys can record an infinite number of frames. This Automatic Data Stream Recording will not disappear when the codes are cleared, and can be saved to your OTC Pegisys or Genisys, printed, transferred to a USB jump drive, and/or your shop computer. NOTE: If the battery in the vehicle is disconnected for any reason, the PCM will loose any Code information it had stored. Of course, all radio, mirror, seat, and HVAC memory will be cleared also. I recommend a Memory Saver if the vehicles’ battery has to be disconnected. Your tool and equipment distributor has a variety of these devices available, at a reasonable cost. Be sure to get one with enough amperage to last as long as the vehicles’ battery is to be disconnected. A Pending Code can erase itself before the light comes on if the problem goes away and stays away for two or three consecutive similar trips. If this happens, no History code or Freeze Frame will be stored. A History code is the medium and long-term storage of a Current code in the computers’ memory, and is strictly for the use of the technician in analyzing a new problem. The History code provides the tech a record of code activity in the recent past. The History code is not an active code; it is a recorded event. The History code carries no Freeze Frame data with it. The History code will self-clear from the computers’ memory after 80 trips (for Continuous Monitors), or 40 trips (for Non-Continuous Monitors). However, some vehicles’ software will keep the History codes for 256 key-starts. Chrysler is an example of key-start count for History code memory. There are four specific levels of codes. These levels indicate the priority of the code, and are explained as follows. Of course, a priority letter is only assigned to a code when there are multiple codes at the same time. Type A codes: The MIL will be triggered on the first trip with the type A codes, and will record a freeze-frame record. Type A’s should be repaired first.

Type B codes: The MIL will trigger on the second or third trip with Type B, and a freeze-frame will be recorded. Type B codes should be addressed after the type A codes have been dealt with. Type C codes: Non-emissions related, these codes will store a History record, and should have a third place priority.

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Type D codes: Non-emissions related, and will not store a freeze frame or a History record. Repair these codes last. Code Categories There are three categories of codes within the OBD II system. They are Electrical, Mechanical, and Rational. Each type of code is specific in its setting criterion. Electrical codes deal with the electrical circuit and its supply source. These codes can be set by a below-standard voltage supply and ground issues, as well as actual circuit failures. An Electrical code will set when extreme or sudden changes in voltage data is noticed when no changes in engine load or circuit operation are observed. An example is a TP sensor which suddenly shows a voltage of less than .2v. This type of fault is monitored by the Comprehensive Components Monitor, and therefore sets a code instantly upon parameter failure. Mechanical codes deal with devices having a mechanical function, such as the passing of fluids or opening and closing of passages. A good example is an EGR passage that may be partially plugged, not allowing the correct volume of exhaust gas to flow. This mechanical code is monitored by the EGR Readiness Monitor. This Monitor uses several EVAP and engine sensors to watch for a change in value outside the pre-set parameters, setting a code on the second trip cycle. Rational codes are set when a sensor does not meet its criterion of operation. An example of a Rational code would be the MAF sensor showing a very high volume of air flow with low engine RPM, a small throttle opening, and no indication of an increase in engine load. This type of MAF PID would indicate an out-of-calibration MAF based on what the other sensors show. In this example, the MAF sensor would not be used by the PCM for fuel control. Each of the above three code types is tested by the Readiness Monitor dedicated to the particular emissions system involved. When a component fails to meet the standard set by the manufacturer during its trip cycle, the component is further monitored for a given period of time. When the component parameters are still not met after the drive cycle is satisfied, a failure is recorded and the MIL is illuminated. The particular components’ parameters are recorded and shown in the “Component Parameters” (Mode 6) section of “Special Tests”. Failure Type Byte DTC There is now a new DTC numbering system in town. An example of this new system is “P0110:1C-AF”. The additional digits at the end of the DTC indicate the “Failure Type Byte”. When a FTB appears on the end of the DTC it will be used by the PCM to give more information about the failure. Many DTC numbers provide enough of a description with the alpha and 4 digits. However, many do not and as a result it is sometimes difficult to determine the exact failure from the DTC without a lot of diagnostic work. An FTB will be added to certain DTC’s when necessary to add a more detail description of the failure leading you to a simpler diagnosis. In the past, P0110 indicated an ‘Intake Air Temperature Sensor Circuit” which may be problems with any of the wiring between the sensor and the PCM, or the sensor itself are at fault. With the new indicator at the end of the fault code (1C-AF), the DTC now gives a more complete description of the failure. This example is indicating the Intake Air Temperature Sensor itself is out of range.

Monitors (OBDII only) Another significant difference between OBD I and II is the onboard diagnostic testing called “Monitors”. The Monitors are active tests of up to eleven electronic systems in the OBD system. Not all OBDII vehicles support all 11 Monitors, however. In fact, two Monitors in particular have never been activated. One is the A/C Monitor, planned before r-134 became the standard mobile refrigerant used in the US. R-134 was judged to be much less harmful to the atmosphere compared to r-12, so the AC monitor has never been used.

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The other Monitor never activated is the Heated Catalyst. The engineering principal behind heating the catalytic converter quickly is the same as heating the O2 sensors: get the cat and the O2 sensors on line within seconds, not minutes. However, the electrical current required to get a catalytic converter up to operating temperature with a heater, and within seconds, is still waiting on the 42v system. This relatively high-voltage electrical system is sure to become a reality one day, but technical and cost challenges have to be overcome first. The Monitors that the OBDII system runs are divided into two groups: Continuous, and Non-Continuous. The Continuous Monitors run their diagnostic tests on three emission control systems continually as long as we have key-on, engine running. These Monitors are: 1 - Misfire 2 - Fuel System 3 - Comprehensive - The Comprehensive Monitor looks for open or shorted circuits, and data that is out of range. All OBDII compliant vehicles run these three Monitors. The Non-Continuous Monitors run their diagnostic tests once per trip, but not continuously. These Monitors include: 1 – Oxygen sensor 2 – Oxygen sensor heater 3 – Catalyst 4 – Heated catalyst (not used) 5 – EGR system (not universally used) 6 – EVAP system 7 – Secondary air system (not universally used) OBD II compliant vehicles run all Continuous Monitors and most of the Non-Continuous monitors. A very few OBD II engines do not need an EGR valve, so do not run that Monitor. Almost all California-compliant systems use secondary air systems, so they will run that Monitor. Most Federal-compliant engines do not. As already stated, when a MIL is illuminated as a result of an emissions related code, an action called “Freeze Frame” is initiated by the PCM. A freeze frame is a snapshot of 8 or 10 PID items. These recordings are required by EPA regulation to capture loop status (open or closed), engine load, coolant temperature, and fuel trim, manifold vacuum (MAP), RPM, and DTC priority. Some PCM’s may add vehicle speed, throttle position, ignition advance, and trips since the MIL was last cleared. Advantage Pegisys , Genisys and Nemisys An extremely useful and unique function of the OTC Pegisys, Genisys, and Nemisys is Automatic DTC Datastream Recording . If an OTC scan tool is communicating with the vehicle while in Datastream when a code happens to set, much of the datastream list will be recorded into the Pegisys, Genisys, or Nemisys memory. This recording will not be erased when the codes are cleared and can contain from 11 to 45 or more PID items. Unlike the freeze frame feature of all OBD II PCM’s, the Genisys DTC Datastream recording captures up to 1,000 frames, and the Pegisys an infinite amount of frames, not just one. Every recorded PID can then be graphed and printed to plain paper using a regular HP type inkjet printer. With available ConnecTech software, all Genisys recordings can be uploaded into your desktop or laptop computer and stored in a file of your choice. The OTC Nemisys offers uploading its recorded information into a computer via an included CD ROM. The OTC Pegisys and Genisys can off-load their recordings onto a USB drive plugged into the tools’ USB port. OBD System Hardware In both the OBDI and II systems, the vehicles’ computer (PCM from now on) deals with three main pieces of hardware: actuators, sensors, and switches. The PCM receives data from sensors and switches, and commands and actuators accordingly. The PCM is programmed by the manufacturer with

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algorithms to compare what it sees to what it expects to see. A pre-determined difference in expected input or output for a given length of time or trip count will trigger a code. However, the PCM is only so smart! It can’t “think outside of the box” (get it?). Verify the code before you start yanking parts. Your OTC scope or meter is your best friend here. Incidentally, some literature and technicians refer to the PCM as the ECM (Electronic Control Module). The two are the same thing. The term ECM, though, is more often used when referring to OBDI systems. A note of interest: PCM’s from the 1980’s until 1993 or so had their operational memories loaded on a replaceable “PROM”. To correct or update one of these early PCM’s you would replace the existing PROM with the correct new one. As a rule, no special tools are needed, except a wrist grounding strap. After 1993, the PCM’s had to be reprogrammed or “reflashed”, to correct or update its operation. The new system, known by its SAE number, J2534, is a web-based reflash method. Great news: OTC will offer the J2534-2 multi-vehicle, all modules reflash program as optional software for the OTC Pegisys. . Modes of Vehicle Operation Both OBD I and II systems operate with two basic modes: open loop then closed loop. Open loop is the mode in use when the engine is first started, and remains in effect until the oxygen sensors (referred to as O2 sensors) begin to operate. In open loop, the fuel mixture is richer than normal so the engine will run smoothly until the ECT (engine coolant temp sensor) tells the PCM the engine has warmed up. This rich mode works like the choke on a carburetor-equipped engine. The HC and CO emissions are very high in this mode, but the O2’s don’t start operating until the exhaust stream reaches 600-650 degrees. When the O2’s do come online, the vehicle switches to the closed loop mode where the O2’s now control the fuel trim. In cold-weather conditions, it may take up to 15 minutes for the O2’s to come online. It’s even possible for working O2’s to kick out if the vehicle idles for a good while allowing the exhaust stream to cool down below 600 degrees. If this happens, the vehicle will return to open loop, and this may increase exhaust emissions. However, some OEM’s use embedded PCM information to take over fuel trim when and if open loop occurs. In about 1990, the OEM’s began installing O2 sensors with heaters built into them. These heaters bring the O2 sensors on line in as little as 15 seconds, and they stay on as long as the engine is running. Since the average trip time is quite short in the US, the tailpipe pollution per trip is reduced significantly, as the vehicle stays in closed loop longer. When OBD II became law in 1996 on most autos and light trucks sold in America, significant changes and improvements were built into the new on-board diagnostic system. One very important change was the addition of a second O2 sensor. This second sensor was located in the exhaust pipe at the outlet of the catalytic converter. V-6 and V-8 engines with true-dual exhaust will have two of each. The additional O2 sensor/s enabled the PCM to closely and accurately monitor the condition and efficiency of the catalytic converter. A P0420 (bank one), or a P0430 (bank two) code will be set if the PCM sees the trailing O2 sensor indicating a rich mixture similar to the front sensor for a given length of time. A brief glossary of a few key OBD system component terms will make the following sections easier to understand. AIR: Also referred to as Secondary Air System (or SAS), used to enhance cat converter efficiency. ECT: Engine Coolant (sensor) Temperature. Sometimes known as CTS: Coolant Temperature Sensor. MAP: Manifold Absolute Pressure. This refers to the pressure (vacuum) in the intake manifold. BARO: Barometric (ambient) pressure sensor, used to set a baseline pressure to calibrate the MAP.

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MAF: Mass Air Flow meter. Not found on all vehicles, the MAF meter is a real-time real-volume meter, which reports actual airflow through the engine. A MAF equipped vehicle can compensate for increases or decreases in intake air flow and exhaust flow and adjust fuel trim accordingly. A MAP-only system cannot do this. The fuel delivery in a MAP-only system is programmed into the PCM by the OEM engineers. This system can only adjust to expected conditions within the factory-programmed values. TPS: Throttle Position Sensor. Note: The new “throttle-by-wire” systems use two sensors, comparing one against the other. VSS: Vehicle Speed Sensor. HO2S: Heated Oxygen Sensor. We’ll just call them O2 sensors. All of them are heated these days. CKP: Crankshaft position sensor, used to report RPM, monitor ignition timing and misfire. CPS: Camshaft Position Sensor, used to identify cylinder #1. EGR: Exhaust Gas Recirculation. KNS: Knock Sensor, used to retard timing to eliminate pre-ignition and spark knock. PID: Parameter Identification – aka Datastream Before we address a few specific repair strategies, let’s look at an overview of what the OBD system is doing during three different trips. The first trip we’ll look at will have the vehicle fully warmed up, and driving at a steady cruise of around 55 or so mph. Steady cruise: The engine is at operating temperature, so the OBD system is in closed-loop. The PCM is relying on inputs from the MAP, TPS, ECT, and CNK, and CPS. The TPS shows only slight variations as the driver (or cruise control) adjusts power to maintain the desired cruise speed. When the driver adds a little power to climb a slight grade or to increase cruise speed slightly, the PCM sees a drop in vacuum (MAP) and a slight rise in TPS voltage. The PCM commands an increase in injector pulse width and retards the timing. This latter adjustment increases dwell time, improving fuel burn. If the vehicle is equipped with a MAF sensor, the MAP is referenced primarily to verify MAF and TPS signals. When the demand for more power is satisfied, the PCM reverses everything it did above. The injector pulse width narrows and the timing advances. These actions return the vehicle to cruise/fuel mileage mode. The O2 sensors are looking at all this activity, and are sending data to the PCM continually. The lead O2 sensor(s) (sensor 1) sends a varying voltage to the PCM several times a second. When the oxygen content of the exhaust stream is rich (low O2 content), the voltage signal sent to the PCM can be close to 1 volt. The full rich signal is actually about 800 mV to 900 mV. When the PCM sees such a signal, it will then narrow the pulse width to full lean, driving the O2 sensor to about 100mV to 200 mV. The length of time the pulse width is held wide or narrow determines the actual fuel delivery. Take note that an O2 sensor should cross between rich and lean at least 7 times a second on OBDII systems at 2500 rpm or greater. O2 sensors will get tired over time and the “cross counts” will fall to a level that hinders efficiency. If you are working on a high-mileage engine with the original O2 sensor(s), it may be money well spent if your customer will authorize you to replace them. Even with no codes in the PCM, fresh O2’s can produce a noticeable improvement in performance, mileage, and emissions. In OBD II, the trailing O2 sensor (sensor 2) is in place to send a signal to the PCM, which should show a much lower content of fuel (high O2) than sensor 1 is reporting. The voltage swings for O2/2 should be between 430mV and 470mV. However, if the exhaust coming out of the cat closely resembles the

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exhaust going in for three consecutive trips, the PCM will store a P0420 (bank one) and/or P0430 code (bank two), and illuminate the MIL. The full rich to full lean cycle may seem to be a rather primitive strategy to handle fuel delivery (called “fuel trim”). However, the catalytic converter has to have it this way. The catalytic converter is designed to oxidize HC and CO into H2O and CO2, and reduce NOx to CO2, H2O, and N2. When the O2 sensor approaches a rich condition the PCM will command a lean injector pulse width, causing combustion to release the unused O2. The catalytic converter will store this O2 in its ceramic substrate. As the O2 sensor approaches a lean condition, the PCM will command a rich injector pulse width, producing CO. This causes the catalyst temperature to rise dramatically, causing the NOx, CO, and HC to vaporize, separating into individual elements of C, H, N, and O. As this occurs, the O2 in the ceramic substrate will oxidize with the C element to form CO2, and a single O element will oxidize with two H elements to become H2O. The N element will then attach with another N to form N2. At steady cruise, the PCM will command the EGR to crack open just a bit. The EGR gas is rich in HC, allowing the PCM to reduce pulse width and alter the ignition timing. The EGR gas causes the HC to oxidize, lowering combustion temperature, much like adding luke-warm water to boiling water until the boiling stops. With these results there will be an improvement in emissions and highway fuel mileage. For a more detailed treatment of the exhaust stream and how you can use it to diagnose driveablilty issues, please see “5 Gas Diagnostics”, by Steve Zack, available at www.genisysotc/training. Acceleration: What happens when the driver wants to accelerate? The PCM strategy calls this “acceleration enrichment mode”. On many V8 and high performance V6 engines, the PCM keeps the O2 sensors in closed loop, even during moderately heavy throttle opening. But many engines will briefly revert to open loop during acceleration, especially WOT. Here’s how acceleration enrichment mode works in those engines: During hard acceleration, the PCM relies on voltage data, first from the TPS, then from the MAF (if equipped), MAP, and CKS/CPS. When the driver drops the hammer, TPS will peg at about 4.3v to 4.7v. The MAP voltage signal will increase (vacuum decrease), and MAF frequency will increase because of the increased air volume. Engine RPM aids the PCM in knowing just how much additional fuel the engine needs to meet the drivers’ power demands. The injector pulse width will increase to keep the air-fuel ratio correct for maximum acceleration. The timing will be retarded and dwell will increase. The increased dwell will provide additional voltage available at the coil to allow a longer oxidation process needed by the spark plug. This process also lessens spark knock. The transmission controller will delay up-shift points to hold a lower gear allowing a higher engine speed for more power and vehicle speed. The shift feel will be firmer and quicker. The torque converter will disengage as necessary to allow more RPM, adding torque and horsepower. The MAP sensor is a very sensitive device, and can even sense a slight change in vacuum between individual cylinders. Because of the MAP’s ability to do this, this sensor is a primary sensor in fuel control. The engineering program that accomplishes this is a seldom talked about PCM strategy called “Timing MAP”. Timing MAP uses vacuum variations between cylinders to adjust individual cylinders’ pulse width as well as control individual ignition timing, keeping the cylinders in relative balance. During hard acceleration, a greater amount of fuel will be used. This sudden increase in fuel will cause an increase in unburned HC and CO. The increases are moderate, and the ignition timing is retarded to compensate. The bigger problem is an increase in NOx due to a sharp increase in combustion temperature. The EGR is used to control combustion temperatures that will cause the formation of NOx. The EGR flow is tightly controlled, so the small amount of EGR diluting the fresh air/fuel mixture will cause no reduction in engine performance. Deceleration lean-out mode: In DLOM, open loop, the PCM utilizes the TPS, MAP and CKP sensors to maintain proper fuel trim. As the driver begins to slow the vehicle, the first input to the PCM, just as in

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acceleration mode, is the TPS. The TPS tells the PCM that the throttle is closed to slow the vehicle. Injector pulse width is decreased and timing is advanced. As air volume decreases, the engine vacuum will rise. MAP sensor voltage will begin to drop, and the PCM continues to command a leaner air fuel mixture. As the vacuum begins to stabilize, the MAP sensor will report that the vacuum level has returned to normal. At this point, the fuel trim reverts to Closed Loop, returning fuel trim settings to the O2 sensors. As mentioned before, OBD II control strategies differ primarily from OBD I by the constant testing and evaluation of the emissions related parameters, sensors, switches, and actuators, and the electrical circuits that serves them. This testing is done by a series of Monitors. All this testing and evaluating is done to ensure the vehicle is performing to the minimum emissions standards set forth by the EPA. To trigger emissions DTC and set the MIL, the component or system must exceed 1.5 times the standard. The government certification test is known as FTP, or Federal Test Procedure. This is an approximately 7 minute version of the 4 minute IM (Inspection and Maintenance) test. The emissions Monitors operate much like a Ford KOER self-test. The difference is that the Monitor testing is performed during a normal driving period with speeds and times similar to the Federal IM240 inspection routine. (IM means “inspection-maintenance”) The IM240 Emissions Test satisfies the EPA standards for emissions system performance. This test procedure consists of a 7-part drive cycle, all done with the drive wheels secured between the two rollers of a chassis dynamometer and a tailpipe probe feeding a gas analyzer. Before the testing is started, the engine is warmed up at least 40 deg. F, reaching 160 deg. F. This step puts the vehicle in closed loop. A Monitor watches for this and will only let the testing begin after these steps are done successfully. A drive cycle occurs over a period of time, with varying speeds and loads. A Trip is a completion from start up to shut down. All Monitors must be run, or the trip is invalid. A “similar trip” is a second trip taken immediately after the first trip. The RPM must be within 375 of the previous trip, and the load must not vary more than 20% of all previous conditions. This “similar trip” is required for any Monitor that requires two or three trip cycles to set two or three flags which will illuminate the MIL. In addition, before the test can begin, the following must be in good operating condition: RPM, ECT, BMAP, and IAT. The Monitors will not run until the vehicle is in Closed Loop mode. The effected Monitor will run if the MIL is on. In addition, the Monitors will not run if the TPS or MAP is fluctuating, indicating varying speed and load. The Acceleration Enrichment or the Deceleration modes cannot be operating. For the first part of the test, Part A, the vehicle idles for exactly 2.5 minutes, with the A/C and rear defroster turned on. During this time, the O2 sensor heaters, the AIR system (if equipped), Misfire, and the EVAP purge Monitors are run. In Part B, the vehicle accelerates to 55 mph at ½ throttle. Here, the misfire, fuel systems, and purge Monitors are run. In Part C the vehicle runs at a steady 35 mph for 3 minutes where the HO2S, EGR, purge, Fuel Trim, and AIR monitors are run. In Part D, the vehicle decelerates from 55 to 20 mph where the EGR, Fuel Trim, and purge Monitors are run. In Part E, the vehicle accelerates to 55 to 60 mph at ¾ throttle. Here the misfire, Fuel Trim, and purge Monitors are run. In Part F, the vehicle operates at a steady 55 to 60 mph for approximately 5 minutes. The catalyst, misfire, HO2S, EGR, purge, and fuel trim monitors are run. In Part G, the vehicle decelerates, ending the test drive cycle while running the purge and EGR monitors. If all Monitors run successfully, the vehicle will pass its emissions testing, and all Monitors will indicate “ready”.

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For OBDII testing, no tailpipe emissions are directly tested. All the information gathered by the test is communicated to the IM machine and the State government by the PCM through the OBDII port under the dash. No dyno is needed for OBD II testing, and the results cannot be successfully tampered with. More on Monitors and how they work Continuous Monitors Misfire Monitor: This Monitor can pick up a misfire in the engine and set one of two codes. A P0300 is a “random misfire” (multiple cylinders). A P03?? is a specific-cylinder id. The Monitor cannot provide the reason for the misfire, e.g. ignition, fuel, or mechanical. The CKP, using an algorithm programmed into the PCM, detects the tiny slowing of the crankshaft when incomplete combustion takes place in the affected cylinder/s. After a sample of from 200 to 1,000 crankshaft revolutions (depending on OEM strategy), if the problem persists, the MIL is turned on. Note: There are actually three separate Misfire Monitors, Types One, Two, and Three. The differences in the three are as follows: The OEM’s and SAE assigned misfire types one and three as “two-trip” misfire monitors. This two-trip strategy acts exactly like all two-trip events. That is, on the first misfire detected by the PCM, the misfire will be recorded as a Pending Code, with no MIL. If the second-trip misfire is detected, the MIL will come on, and the code will be stored as active. A Type Two misfire indicates a much more severe misfire problem. As such, the MIL will be commanded on during misfire trip one. The one-trip MIL will be either steady or flashing. If the MIL is flashing, the catalytic converter is in imminent danger of severe damage. Diagnose and repair the cause of a flashing MIL immediately. It can happen that a flashing MIL can revert to a steady presentation. If this happens, there is no longer an immediate danger to the cat. However, the severe problem can suddenly reoccur, so do not let the vehicle out of the shop without repairing the misfire problem first. Fuel System Monitor: This Monitor verifies that the O2 sensor cross-counts are quick enough, at least 7 times per second at 2,500 rpm or more. This applies in both short-term and long-term fuel trim modes. This Monitor requires two consecutive similar trips to set the MIL Comprehensive Component Monitor (CCM): This Monitor scans for open or short circuits and electrical parameters that are out of range. This Monitor is either a one or two trip MIL, depending on the component. Non-Continuous Monitors HO2S Monitor: Closed loop will occur only when the exhaust stream reaches 600-650 degrees. When closed loop occurs, this Monitor forces the fuel trim to “full rich” and watches for a voltage response of

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at least 600mV. The Monitor then forces the mixture to “full lean”, and watches for the voltage to go below 300mV. If the voltages are inadequate, or the cross-counts are too slow, an MIL will be set. This Monitor requires two similar trips to set the MIL. Catalyst Monitor: This Monitor will only run when the vehicle is running at a cruise speed for a minimum of 3 to 6 minutes. The Monitor watches the cross rates of HO2S 1 compared to HO2S 2. The downstream O2 must not cross more that 30% of the upstream O2. Mostly, HO2S 2 will stay in the “lean” range, reflecting a catalyst that is burning the residual HC and CO out of the exhaust stream. This Monitor requires three similar trips to set an MIL if a problem exists. EGR Monitor: Steady cruise or deceleration is required to run this Monitor. When the PCM commands the EGR to open, total intake manifold volume will be increased. The MAP watches for a vacuum drop when this happens. If this vac drop is not detected by the MAP, a MIL will be commanded after two similar trips. Readiness Status Readiness Status is a test that reviews the condition of the Monitors. If the Readiness Status records a Monitor that did not run because of an active or pending code, that Monitor will show “not ready”. When the condition that caused the failure is corrected, and the vehicle is driven in accordance with the applicable Drive Cycle, the Monitor will then run its test, and show the message, “ready”. The State OBDII IM programs require all Readiness Monitors to run successfully before a vehicle can pass the IM test. However, some states will allow two Monitors to read “not ready” on 1999 and older vehicles and one “not ready” on 2000 and newer vehicles, as long as the MIL is not on. Check your State regulations for details. If the MIL is illuminated, the vehicle will not pass. Freeze Frame This is a “snapshot” of one frame of data for several vehicle parameters that existed when the MIL was triggered. The PCM is required to record the following items: Loop Status, Calculated Load (expressed as a percent of 100), ECT, Short and Long Fuel Trim, MAP, RPM, and VSS. Some vehicle manufacturers add a few items to this recording such as TPS, IAT, and MAF. Note: The Freeze Frame is set the instant the MIL is illuminated. Keep in mind that the PCM always delays setting the MIL until it is satisfied the problem is persistent (this is known as Enable Criteria). This may take several seconds to several minutes for the Enable Criteria to set the MIL. Therefore, the Freeze Frame may reflect conditions that may no longer be current. Mode Six Mode 6 is a very sophisticated function that displays, along with min/max specs, the test results of each emission Monitor. Mode 6 information is the actual test result of the individual drive-cycle readiness tests of both continuous and non-continuous monitors. During each drive cycle, the PCM will monitor and evaluate the Mode 6 test results and store them in the KAM (keep alive memory). The PCM uses a value called the “Exponentially Weighted Moving Average” or EWMA, to judge whether the test result is within the acceptable parameters. As the Monitor data is gathered by the PCM, the EWMA value is applied to the test, causing the points of the data to become more important as the problem becomes closer to failing the test. This allows for the latest test results to be of greater value in determining pass or fail conditions. Note: be sure to read your Mode 6 info before you switch the vehicle off. Many vehicles may reset Mode 6 at key-off. Most aftermarket scan tools cannot read or display Mode 6 information at all. The OTC Pegisys and the Genisys do a remarkable job of displaying the “TID” (test i.d.) and the “CID” (component i.d.) test information. When the OEMs’ began the switch to CAN in 2003 they changed the name of Mode 6 “CID”

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to “MID” (Monitor ID). You will find Component Parameters on the Diagnostic Menu of the Pegisys and Genisys. Scroll to “Component Parameters (mode 6)”, and press “enter”. Then scroll down through all the Monitors. Many of the Mode 6 data PIDS are only given a number and not identified in plain English. The OEM’s assign these TID and CID numbers to suit them and do not readily give out this information. And there is no standard for what a TID or CID number refers to. OTC is identifying and adding English explanations to these numbers as quickly as we can learn them. The website “iatn.net” is a wealth of Mode 6 information, especially for Ford and Toyota. IATN.net is available to anyone with a computer. To cloud the issue further, the actual test result numbers may be given not in the familiar decimal system, but in a scientific number system called “hexadecimal”. Hexadecimal values are reported with a combination of numbers and letters, and are identified as Hexadecimal with a dollar symbol ($) prefix. If you have identified what TID and CID you are dealing with, your standard Windows computer has a calculator that will convert Hexadecimal to decimal. To do this translation, click All Programs, and then click on Accessories. Next, select Calculator, and then click on View and select “Scientific”. Next, click on “Hex”. Then enter the Hexadecimal value (let’s use 33E as an example) in the value box. Then select the “Dec” button. Voila! 33E becomes 830! Compare 830 to the min/max limit in the Mode 6 test to determine the health of the Monitor results.

Incidentally, GM has a DTC function called “Failure Records”, for OBD II vehicles. This info is essentially the same as Mode 6, and is easily read and understood. The information given in Failure Records, as well as in Mode 6, can be used to predict if a system is about to store a two trip failure before the MIL is set. This info can be used as repair verification, saving you a lot of time or even a comeback. In Part Two of this series, we will delve into several repair strategies on the three domestic vehicle makes. Of course, our examples will also apply to most OBDII vehicles, domestic and otherwise. These examples are all based on real-world, common-failure events that you should find familiar, and we hope our repair ideas will be helpful. Stay tuned…

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OBDII and Emissions Testing

Are you up to speed on OBD II? You should be because starting in 2002, a number of states have announced plans to change their emissions testing programs over to OBD II. Instead of doing a tailpipe emissions check on a dynamometer, an OBD II check is a simple plug-in test that takes only seconds. What’s more, OBD II will detect emissions problems that might not cause a vehicle to fail a tailpipe test - which means emissions test failures under the OBD II test programs are expected to be significantly higher. The second-generation self-diagnostic emissions software has been required on all new vehicles sold in this country since model year 1996, including all imports. OBD II is a powerful diagnostic tool that can give you insight into what’s actually happening within the engine control system. Unlike earlier OBD systems that set a DTC when a sensor circuit shorts, opens or reads out of range, OBD II is primarily emissions-driven and will set codes anytime a vehicle’s emissions exceed the federal limit by 1.5 times.It also will set codes if there is a gross sensor failure, but some types of sensor problems won’t always trigger a code. Consequently, the Check Engine light on an OBD II-equipped vehicle may come on when there is no apparent driveability problem, or it may not come on even though a vehicle is experiencing a noticeable driveability problem. The determining factor as to whether or not the Check Engine light comes on is usually the problem’s effect on emissions. In many instances, emissions can be held in check, despite a faulty sensor, by adjusting fuel trim. So as long as emissions can be kept below the limit, the OBD II system may have no reason to turn on the light. CHECK ENGINE LIGHT The "Malfunction Indicator Lamp" (MIL), which may be labeled "Check Engine" or "Service Engine Soon" or a symbol of an engine with the word "Check" in the middle, is supposed to alert the driver when a problem occurs. Depending on how the system is configured and the nature of the problem, the lamp may come on and go off, remain on continuously or flash - all of which can be very confusing to the motorist because he has no way of knowing what the light means. Is it a serious problem or not? If the engine seems to be running okay, the motorist may simply ignore the light. With OBD II, the Check Engine light will come on only for emissions-related failures. A separate warning light must be used for other non-emissions problems such as low oil pressure, charging system problems, etc. If the light is on because of a misfire or a fuel delivery problem, and the problem does not recur after three drive cycles (under the same driving conditions), the Check Engine light may go out. Though you might think the vehicle has somehow healed itself, the intermittent problem may still be there waiting to trigger the light once again when conditions are right. Whether the light goes out or remains on, a code will be set and remain in the computer’s memory to help you diagnose the fault. With some exceptions, the OBD II warning lamp will also go out if a problem does not recur after 40 drive cycles. A drive cycle means starting a cold engine and driving it long enough to reach operating temperature. The diagnostic codes that are required by law on all OBD II systems are "generic" in the sense that all vehicle manufacturers use the same common code list and the same 16-pin diagnostic connector. Thus, a P0302 misfire code on a Nissan means the same thing on a Honda, Toyota or Mercedes-Benz. But each vehicle manufacturer also has the freedom to add their own "enhanced" codes to provide even more detailed information about various faults. Enhanced codes also cover non-emission related failures that occur outside the engine control system. These include ABS codes, HVAC codes, air bag codes and other body and electrical codes.

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The second character in an OBD II will be a zero if it’s a generic code, or a "1" if it’s a dealer enhanced code (specific to that particular vehicle application). The third character in the code identifies the system where the fault occurred. Numbers 1 and 2 are for fuel or air metering problems, 3 is for ignition problems or engine misfire, 4 is for auxiliary emission controls, 5 relates to idle speed control problems, 6 is for computer or output circuit faults, and 7 and 8 relate to transmission problems. Codes can be accessed and cleared using an OBDII scan tool such as AutoTap. MISFIRE DETECTION If an emissions problem is being caused by engine misfire, the OBD II light will flash as the misfire is occurring. But the light will not come on the first time a misfire problem is detected. It will come on only if the misfire continues during a second drive cycle and will set a P0300 series code. A P0300 code would indicate a random misfire (probably due to a vacuum leak, open EGR valve, etc.). If the last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for example, would tell you cylinder number two is misfiring. Causes here would be anything that might affect only a single cylinder such as a fouled spark plug, a bad coil in a coil-on-plug ignition system or distributorless ignition system with individual coils, a clogged or dead fuel injector, a leaky valve or head gasket. The OBD II system detects a misfire on most vehicles by monitoring variations in the speed of the crankshaft through the crankshaft position sensor. A single misfire will cause a subtle change in the speed of the crank. OBD II tracks each and every misfire, counting them up and averaging them over time to determine if the rate of misfire is abnormal and high enough to cause the vehicle to exceed the federal emissions limit. If this happens on two consecutive trips, the Check Engine light will come on and flash to alert the driver when the misfire problem is occurring. Misfire detection is a continuous monitor, meaning it is active any time the engine is running. So too is the fuel system monitor that detects problems in fuel delivery and the air/fuel mixture, and something called the "comprehensive monitor" that looks for gross faults in the sensors and engine control systems. These monitors are always ready and do not require any special operating conditions. Other OBD II monitors are only active during certain times. These are the "non-continuous" monitors and include the catalytic converter efficiency monitor, the evaporative system monitor that detects fuel vapor leaks in the fuel system, the EGR system monitors, the secondary air system monitor (if the vehicle has such a system), and the oxygen sensor monitors.On some 2000 and newer vehicles, OBD II also has a thermostat monitor to keep an eye on the operation of this key component. The thermostat monitor will be required on all vehicles by 2002. On some 2002 model-year vehicles, there also is a new PCV system monitor, which will be required on all vehicles by 2004. The catalytic converter monitor keeps an eye on converter efficiency by comparing the outputs from the upstream and downstream oxygen sensors. If the converter is doing its job, there should be little unburned oxygen left in the exhaust as it exits the converter. This should cause the downstream O2 sensor to flatline at a relatively fixed voltage level near maximum output. If the downstream O2 sensor reading is fluctuating from high to low like the front sensor, it means the converter is not functioning.The Check Engine light will come on if the difference in O2 sensor readings indicates hydrocarbon (HC) readings have increased to a level that is 1.5 times the federal limit. For 1996 and newer vehicles that meet federal Low Emission Vehicles (LEV) requirements, the limit allows only 0.225 grams per mile (gpm) of HC - which is almost nothing. Converter efficiency drops from 99 percent when it is new to around 96 percent after a few thousand miles. After that, any further drop in efficiency may be enough to turn on the Check Engine light. We’re talking about a very sensitive diagnostic monitor.

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The EVAP system monitor checks for fuel vapor leaks by performing either a pressure or vacuum test on the fuel system. For 1996 through 1999 vehicles, the federal standard allows leaks up to the equivalent of a hole .040 inches in diameter in a fuel vapor hose or filler cap. For 2000 and newer vehicles, the leakage rate has been reduced to the equivalent of a .020 in. diameter hole, which is almost invisible to the naked eye but can be detected by the OBD II system. Finding these kinds of leaks can be very challenging. READINESS FLAGS An essential part of the OBD II system are the "readiness flags" that indicate when a particular monitor is active and has taken a look at the system it is supposed to keep watch over. The misfire detection, fuel system and continuous system monitors are active and ready all the time, but the non-continuous monitors require a certain series of operating conditions before they will set - and you can’t do a complete OBD II test unless all of the monitors are ready. To set the converter monitor, for example, the vehicle may have to be driven a certain distance at a variety of different speeds. The requirements for the various monitors can vary considerably from one vehicle manufacturer to another, so there is no "universal" drive cycle that will guarantee all the monitors will be set and ready. As a general rule, doing some stop-and-go driving around town at speeds up to about 30 mph followed by five to seven minutes of 55 mph plus highway speed driving will usually set most or all of the monitors (the converter and EVAP system readiness monitors are the hardest ones to set). So if you’re checking the OBD II system and find a particular monitor is not ready, it may be necessary to test drive the vehicle to set all the monitors. The Environmental Protection Agency (EPA) realized this shortcoming in current generation OBD II systems. So, when it created the rules for states that want to implement OBD II testing in place of tailpipe dyno testing, it allows up to two readiness flags to not be set prior to taking an OBD II test on 1996 to 2000 vehicles, and one readiness flag not to be set on 2001 and newer vehicles. You can use the AutoTap OBDII scantool to check that your readiness flags are set before having your vehicle emissions-tested. This can save you the aggrevation of being sent off to drive around and come back later. Some import vehicles have known readiness issues. Many 1996-’98 Mitsubishi vehicles will have monitors that read "not ready" because setting the monitors requires very specific drive cycles (which can be found in their service information). Even so, these vehicles can be scanned for codes and the MIL light without regard to readiness status.On 1996 Subarus, turning the key off will clear all the readiness flags. The same thing happens on 1996 Volvo 850 Turbos. This means the vehicle has to be driven to reset all the readiness flags. On 1997 Toyota Tercel and Paseo models, the readiness flag for the EVAP monitor will never set, and no dealer fix is yet available. Other vehicles that often have a "not ready" condition for the EVAP and catalytic converter monitors include 1996-’98 Volvos, 1996-’98 Saabs, and 1996-’97 Nissan 2.0L 200SX models. OBD II TEST An official OBD II emissions test consists of three parts:

1. An inspector checks to see if the MIL light comes on when the key is turned on. If the light does not come on, the vehicle fails the bulb check.

2. A scanner similar to AutoTap is plugged into the diagnostic link connector (DLC), and the system is

checked for monitor readiness. If more than the allowed number of monitors are not ready, the vehicle is rejected and asked to come back later after it has been driven sufficiently to set the readiness flags. The scanner also checks the status of the MIL light (is it on or off?), and downloads any fault codes that may be present.If the MIL light is on and there are any OBD II codes present, the vehicle fails the test and must be repaired. The vehicle also fails if the DLC is missing, has been tampered with or fails to provide any data.

3. As a final system check, the scanner is used to command the MIL lamp on to verify it is taking

commands from the onboard computer. If the OBD II light is on, or a vehicle has failed an OBD II

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emissions test, your first job is to verify the problem. That means plugging into the OBD II system, pulling out any stored codes and looking at any system data that might help you nail down what’s causing the problem. Long-term fuel trim data can provide some useful insight into what’s going on with the fuel mixture. If long-term fuel trim is at maximum, or you see a big difference in the numbers for the right and left banks of a V6 or V8 engine, it would tell you the engine control system is trying to compensate for a fuel mixture problem (possibly an air leak, dirty injectors, leaky EGR valve, etc.).

OBD II also provides "snap shot" or "freeze frame" data, which can help you identify and diagnose intermittent problems. When a fault occurs, OBD II logs a code and records all related sensor values at that moment for later analysis. Once you’ve pinpointed the problem and hopefully replaced the faulty component, the final step is to verify that the repair solved the problem and that the OBD II light remains off. This will usually require a short test drive to reset all the readiness monitors and run the OBD II diagnostic checks. OBD II TOOLS & EQUIPMENT You can’t work on OBD II systems without some type of OBD II-compliant scanner. The AutoTap OBDII Scan Tool is available in both PC/laptop versions and Palm PDA versions. The computing power and display of a PC or Palm gives AutoTap a much broader range of features than the older style hand-held scantools.

The OBDII Home Page http://www.obdii.com

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OBDII: PAST, PRESENT & FUTURE

All 1996 and newer model year passenger cars and light trucks are OBDII-equipped, but the first applications were actually introduced back in ‘94 on a limited number of vehicle models. What makes OBDII different from all the self-diagnostic systems that proceeded it is that OBDII is strictly emissions oriented. In other words, it will illuminate the Malfunction Indicator Lamp (MIL) anytime a vehicle’s emissions exceed 1.5 times the federal test procedure (FTP) standards for that model year of vehicle. That includes anytime random misfires cause an overall rise in HC emissions, anytime the operating efficiency of the catalytic converter drops below a certain threshold, anytime the system detects air leakage in the sealed fuel system, anytime a fault in the EGR system causes NOX emissions to go up, or anytime a key sensor or other emission control device fails. In other words, the MIL light may come on even though the vehicle seems to be running normally and there are no real driveability problems. The main purpose of the MIL lamp on an OBDII-equipped vehicle, therefore, is to alert you when your vehicle is polluting so you’ll get their emission problems fixed. But as we all know, its easy to ignore warning lamps— until steam is belching from under the hood or the engine is making horrible noises. That’s why regulators want to incorporate OBDII into existing and enhanced vehicle emissions inspection programs. If the MIL lamp is found to be on when a vehicle is tested, it doesn’t pass even if its tailpipe emissions are within acceptable limits. WHY OBDII? The problem with most vehicle inspection programs is that they were developed back in the 1980s to identify "gross polluters." The tests were designed primarily to measure idle emissions on carbureted engines (which are dirtiest at idle), and to check for only two pollutants: unburned hydrocarbons (HC) and carbon monoxide (CO). The pass/fail cut points that were established for the various model years were also made rather lenient to minimize the number of failures. Consequently, a lot of late model vehicles that shouldn’t be passing an emissions test are getting through anyway. Efforts to upgrade vehicle inspection programs to the new I/M 240 standards have stalled because of a lack of public and political support. The I/M 240 program would have required "loaded-mode" emissions testing on a dyno while the vehicle was driven at various speeds following a carefully prescribed driving trace. While this was going on, the tailpipe gases would be analyzed to check not only for total emissions. The total emissions for the entire 240-second driving cycle would then be averaged for a composite emission score that determines whether or not the vehicle passed the test. Also included would be an evaporative purge flow test to measure the flow rate of the canister purge valve, and an engine off pressure test of the evaporative emission control system to check the fuel tank, lines and cap for leaks. The I/M 240 program was to have been required in most areas of the country that don’t meet national ambient air quality (NAAQ) standards. But after the program faltered in Maine, most states balked and only Colorado went ahead with the program. The cost and complexity of the I/M 240 program combined with less than enthusiastic public acceptance doomed it from the start. So it’s now up to the individual states to come up with alternative plans for improving their air quality. An important element in many of those plans is OBDII. A SHORT HISTORY WITH FAR REACHING IMPLICATIONS The origins of OBDII actually date back to 1982 in California, when the California Air Resources Board (ARB) began developing regulations that would require all vehicles sold in that state starting in 1988 to have an onboard diagnostic system to detect emission failures. The original onboard diagnostic system (which has since become known as OBDI) was relatively simple and only monitored the oxygen sensor, EGR system, fuel delivery system and engine control module.

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OBDI was a step in the right direction, but lacked any requirement for standardization between different makes and models of vehicles. You still had to have different adapters to work on different vehicles, and some systems could only be accessed with costly "dealer" scan tools. So when ARB set about to develop standards for the current OBDII system, standardization was a priority: a standardized 16-pin data link connector (DLC) with specific pins assigned specific functions, standardized electronic protocols, standardized diagnostic trouble codes (DTCs), and standardized terminology. Another limitation of OBDI was that it couldn’t detect certain kinds of problems such as a dead catalytic converter or one that had been removed. Nor could it detect ignition misfires or evaporative emission problems. Furthermore, OBDI systems would only illuminate the MIL light after a failure had occurred. It had no way of monitoring progressive deterioration of emissions-related components. So it became apparent that a more sophisticated system would be required. The California Air Resources Board eventually developed standards for the next generation OBD system, which were proposed in 1989 and became known as OBDII. The new standards required a phase-in starting in 1994. The auto makers were given until the 1996 model year to complete the phase-in for their California vehicles. Similar standards were incorporated into the federal Clean Air Act in 1990 which also required all 49-state vehicles to be OBDII equipped by 1996 -- with one loophole. The OBDII systems would not have to be fully compliant until 1999. So some 1996 OBDII systems may lack one of the features normally required to meet the OBDII specs, such as the evaporative emissions purge test. EARLY OBDII APPLICATIONS 1994 vehicles equipped with the early OBD II systems include Buick Regal 3800 V6, Corvette, Lexus ES3000, Toyota Camry (1MZ-FE 3.0L V6) and T100 pickup (3RZ-FE 2.7L four), Ford Thunderbird & Cougar 4.6L V8, and Mustang 3.8L V6.1995 vehicles with OBDII include Chevy/GMC S, T-Series pickups, Blazer and Jimmy 4.3L V6, Ford Contour & Mercury Mystique 2.0L four & 2.6L V6, Chrysler Neon, Cirrus and Dodge Stratus, Eagle Talon 2.0L DOHC (nonturbo), and Nissan Maxima and 240 SX. Not all of these early applications are fully OBDII compliant, but do include the major diagnostic features of the current system. OBDII HARDWARE UPGRADES Don’t think for a moment that OBDII is just a fancier version of self-diagnostic software. It’s that and much, much more.OBDII-equipped vehicles typically have:

• Twice the number of oxygen sensors as non-OBDII vehicles(most of which are heated O2 sensors). The additional O2 sensors are located downstream of the catalytic converter.

• More powerful powertrain control modules, with either16-bit (Chrysler) or 32-bit (Ford & GM) processors

to handle up to 15,000 new calibration constants that were added by OBDII.

• Electronically Erasable Programmable Read Only Memory(EEPROM) chips that allows the PCM to be reprogrammed with revised or updated software changes using a terminal link or external computer.

• A modified evaporative emission control systems with a diagnostic switch for purge testing, or an

enhanced EVAP system with a vent solenoid, fuel tank pressure sensor and diagnostic test fitting,

• More EGR systems with a linear EGR valve that is electronically operated and has a pintle position sensor.

• Sequential fuel injection rather than multiport or throttle body injection. Both a MAP sensor and MAF

sensor for monitoring engine load and airflow.

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TOOLING UP FOR OBDII To work on your OBDII-equipped vehicle, you’ll need an OBDII scan tool such as AutoTap for PC or Palm PDA. THAT PESKY MIL LAMP Most technicians are pretty familiar with the operation of the "Check Engine" or "Malfunction Indicator Lamp" (MIL) on late model vehicles. But on OBDII-equipped vehicles, it may seem like the MIL lamp has a mind of its own. On ‘96 General Motors J-, N- and H-body cars, several rental fleets have encountered problems with the MIL lamp coming on because motorists and fleet personnel haven’t been using the correct refueling procedure when filling the fuel tank with gas. On these cars, the OBDII system applies vacuum to the evaporative emissions control system to check for air leakage. If the gas cap isn’t tight or the tank is filled while the key is on or the engine is idling, it can trigger a false P0440 code causing the MIL light to come on. GM has not issued a technical service bulletin on the problem, but is advising its dealers and fleet customers to reflash the EEPROM with revised OBDII programming that waits to check the evaporative emissions system until the vehicle is in motion. Bad gas has also been causing some false MIL lights. When the vehicle is diagnosed, the technician finds a P0300 random misfire code which would normally be set by a lean misfire condition due to a vacuum leak, low fuel pressure, dirty injectors, etc., or an ignition problem such as fouled plugs, bad plug wires, weak coil, etc. The OBDII self-diagnostics tracks misfires by individual cylinder, and considers up to a 2% misfire rate as normal. But water in the gas or variations in the additive package in reformulated gasoline in some areas of the country can increase the misfire rate to the point where it triggers a code. To minimize the occurrence of false MIL lamps, the OBDII system is programmed so that the MIL lamp only comes on if a certain kind of fault has been detected twice under the same driving conditions. With other faults (those that typically cause an immediate and significant jump in emissions), the MIL light comes on after only a single occurrence. So to correctly diagnose a problem, it’s important to know what type of code you’re dealing with. Type A diagnostic trouble codes are the most serious and will trigger the MIL lamp with only one occurrence. When a Type A code is set, the OBDII system also stores a history code, failure record and freeze frame data to help you diagnose the problem. Type B codes are less serious emission problems and must occur at least once on two consecutive trips before the MIL lamp will come on. If a fault occurs on one trip but doesn’t happen again on the next trip, the code won’t "mature" and the light will remain off. When the conditions are met to turn on the MIL lamp, a history code, failure record and freeze frame data are stored the same as with Type A codes. A drive cycle or trip, by the way, is not just an ignition cycle, but a warm-up cycle. It is defined as starting the engine and driving the vehicle long enough to raise the coolant temperature at least 40 degrees F (if the startup temperature is less than 160 degrees F). Once a Type A or B code has been set, the MIL will come on and remain on until the component that failed passes a self-test on three consecutive trips. And if the fault involved something like a P0300 random misfire or a fuel balance problem, the light won’t go out until the system passes a self-test under similar operating conditions (within 375 rpm and 10% of load) that originally caused it to fail. That’s why the MIL lamp won’t go out until the emissions problem has been repaired. Clearing the codes with your AutoTap scan tool or disconnecting the powertrain control module’s power supply won’t prevent the lamp from coming back on if the problem hasn’t been fixed. It may take one or more driving cycles to reset the code, but sooner or later the MIL lamp will go back on if the problem is still there. Likewise, the MIL won’t necessarily go on if you intentionally disconnect a sensor. It depends on the priority ranking of the sensor (how it affects emissions), and how many driving cycles it takes for the OBDII diagnostics to pick up the fault and set a code.

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As for Type C and D codes, these are non-emissions related. Type C codes can cause the MIL lamp to come on (or illuminate another warning lamp), but Type D codes do not cause the MIL lamp to come on. RUNNING AN OBDII DRIVE CYCLE Suppose you’ve "fixed" an emissions problem on your OBDII-equipped vehicle. How can you check your work? By performing what’s called an "OBDII drive cycle." The purpose of the OBDII drive cycle is to run all of the onboard diagnostics. The drive cycle shold be performed after you’ve erased any trouble codes from the PCM’s memory, or after the battery has been disconnected. Running through the drive cycle sets all the system status "flags" so that subsequent faults can be detected. The OBDII drive cycle begins with a cold start (coolant temperature below 122 degrees F and the coolant and air temperature sensors within 11 degrees of one another). NOTE: The ignition key must not be on prior to the cold start otherwise the heated oxygen sensor diagnostic may not run.

1. As soon as the engine starts, idle the engine in drive for two and a half minutes with the A/C and rear defrost on. OBDII checks oxygen sensor heater circuits, air pump and EVAP purge.

2. Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle. OBDII checks for ignition

misfire, fuel trim and canister purge.

3. Hold at a steady state speed of 55 mph for three minutes. OBDII monitors EGR, air pump, O2 sensors and canister purge.

4. Decelerate (coast down) to 20 mph without braking or depressing the clutch. OBDII checks EGR and

purge functions.

5. Accelerate back to 55 to 60 mph at ¾ throttle. OBDII checks misfire, fuel trim and purge again.

6. Hold at a steady speed of 55 to 60 mph for five minutes. OBDII monitors catalytic converter efficiency, misfire, EGR, fuel trim, oxygen sensors and purge functions.

7. Decelerate (coast down) to a stop without braking. OBDII makes a final check of EGR and canister

purge.

BEYOND OBDII OBDII is a very sophisticated and capable system for detecting emissions problems. But when it comes to getting motorists to fix emission problems, it’s no more effective than OBDI. Unless there’s some means of enforcement, such as checking the MIL light during a mandatory inspection, OBDII is just another idiot light. Currently under consideration are plans for OBDIII, which would take OBDII a step further by adding telemetry. Using miniature radio transponder technology similar to that which is already being used for automatic electronic toll collection systems, an OBDIII-equipped vehicle would be able to report emissions problems directly to a regulatory agency. The transponder would communicate the vehicle VIN number and any diagnostic codes that were present. The system could be set up to automatically report an emissions problem via a cellular or satellite link the instant the MIL light comes on, or to answer a query from a cellular, satellite or roadside signal as to its current emissions performance status. What makes this approach so attractive to regulators is its effectiveness and cost savings. Under the current system, the entire vehicle fleet in an area or state has to be inspected once every year or two to identify the 30% or so vehicles that have emissions problems. With remote monitoring via the onboard telemetry on an OBDIII-equipped vehicle, the need for periodic inspections could be eliminated because only those vehicles that reported problems would have to be tested.

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On one hand, OBDIII with its telemetry reporting of emission problems would save consumers the inconvenience and cost of having to subject their vehicle to an annual or biennial emissions test. As long as their vehicle reported no emission problems, there’d be no need to test it. On the other hand, should an emissions problem be detected, it would be much harder to avoid having it fixed—which is the goal of all clean air programs anyway. By zeroing in on the vehicles that are actually causing the most pollution, significant gains could be made in improving our nation’s air quality. But as it is now, polluters may escape detection and repair for up to two years in areas that have biennial inspections. And in areas that have no inspection programs, there’s no way to identify such vehicles. OBDIII would change all that. The specter of having Big Brother in every engine compartment and driving a vehicle that rats on itself anytime it pollutes is not one that would appeal to many motorists. So the merits of OBDIII would have to be sold to the public based on its cost savings, convenience and ability to make a real difference in air quality. Even so, any serious attempt to require OBDIII in the year 2000 or beyond will run afoul of Fourth Amendment issues over rights of privacy and protection from government search and seizure. Does the government have the right to snoop under your hood anytime it chooses to do so, or to monitor the whereabouts of your vehicle? These issues will have to be debated and resolved before OBDIII stands a chance of being accepted. Given the current political climate, such drastic changes seem unlikely. Another change that might come with OBDIII would be even closer scrutiny of vehicle emissions. The misfire detection algorithms currently required by OBDII only watch for misfires during driving conditions that occur during the federal driving cycle, which covers idle to 55 mph and moderate acceleration. It does not monitor misfires during wide open throttle acceleration. Full range misfire detection will be required for 1997 models. OBDIII could go even further by requiring "fly-by-wire" throttle controls to reduce the possibility of misfires on the coming generation of low emission and ultra low emission vehicles.So until OBDIII winds its way through the regulatory process, all we have to worry about is diagnosing and repairing OBDII-equipped vehicles and all the non-OBD vehicles that came before them.

AutoTap – OBDII Automotive Diagnostic Tool http://www.autotap.com

Introduction To OBD IIIntroduction To OBD II

George E. Pataki Raymond P. Martinez Erin M. CrottyGovernor DMV Commissioner DEC Commissioner

Introduction

Onboard Diagnostics, OBDOBD, technology benefits motorists, technicians and the environment by monitoring a vehicles performance every time it is driven,

identifying performance and emissions problems immediately and providing technicians with information to help

them quickly and accurately diagnose and repair malfunctions

Early OBD Systems (Pre – 1996)

The first OBD systems appeared on vehicles in the 1980’s (OBD I) and monitored fuel, ignition and emissions systems components. When a fault was found a code was stored in the vehicles onboard computer and in many instances a “Check Engine” light was lit to alert the driver. Technicians could connect to the computer and see what codes had been set and make a diagnosis of the problem

Early OBD Systems (Pre – 1996)(Continued)

While the concept was a good one, several practical problems were found in actual use…..No Standardization of data link connectors – a different one needed for each manufacturers vehiclesTrouble codes not consistent between manufacturersNo standardization of emissions control device and system names between manufacturersCriteria to light check engine light not consistent between manufacturersType of stored information in vehicles computer varied from manufacturer to manufacturer

OBD II SystemsNoting that OBD systems were valuable technology in maintaining good performance and lower emissions in

vehicles, the U.S. EPA developed regulations that required all vehicles meet specific and consistent

standards for OBD systems, OBD IIOBD II, by 1996 These regulations resulted in standardization of,

Data Link Connector and location in vehicleTerminology for vehicle emissions control componentsDiagnostic trouble codesFreeze Frame – storage of engine conditions at time a DTC is setRequirements for lighting MIL (Check Engine Light)Determination and recording of readiness status of system monitors

DLCStandardized Data Link Connector

Allows generic scan tool to be used on all OBD II equipped systems.Contains 16 terminals – some OBD II dedicated and some manufacturer discretionary.Location of DLC standardized.

Standardized TerminologyDifferent manufacturers used different names / acronyms for essentially the same components / systems. The Society of Automotive Engineers,

S.A.E., developed standardized terminology for engine and emissions systems.See Glossary in Inspectors Reference Guidefor examples.

OBD Failure Criteria

Reasons for failing an OBD II inspectionMIL does not light with key on – engine off (KOEO)MIL is lit with the key on - engine running (KOER)Scan tool indicates DTC’s, and MIL is commanded on by the PCM, even if it is not litMore than the allowable number of monitors are found to be “not ready”DLC is missing or damaged – communications failure

MILMalfunction Indicator Light

The MIL is a light on the dashboard to alert the driver of an emissions related problem. The MIL will be lit if one of the following conditions is present,

Severe misfire which could cause catalytic converter damage will cause it to flash on and off.A steadily lit MIL indicates a DTC has been set.

The OBD II system can turn the MIL off on it’s own if it detects that the cause of the MIL being lit has been corrected.

DTCsDiagnostic Trouble Codes

Prior to OBD II each manufacturer had it’s own list of trouble codes. Under OBD II all manufacturers must use a universal 5 digit code system.

DTC’sDiagnostic Trouble Codes (Continued)

There are two types of DTC’s, 1 trip DTC’s and 2 trip DTC’s

A 1 trip DTC is for a condition that requires immediate attention such as a catalyst damaging misfire.

A 2 Trip DTC is one that a condition must be found during 2 consecutive trips such as an EGR fault.

Most Monitors do not set a DTC and light the MIL when a vehicle fails a test for the first time during a DRIVE CYCLE. If a test is failed on a second consecutive DRIVE CYCLE the MIL will light and a DTC is stored in the vehicles powertrain control module (PCM).

System Monitors & Readiness Status

One of the features of OBD II testing is that the vehicle need not be warmed up or pre-conditioned before doing the test.The OBD system periodically runs what are called MONITORS to determine if the various emissions control devices and systems are READY and able to operate as they were designed.Some Monitors are CONTINUOUS monitors and some are NON-CONTINUOUS monitors.Monitors are run during what are calledDRIVE CYCLES

Continuous & Non-Continuous Monitors

Some vehicle components are continuously tested by OBD II while others are only tested under certain operating conditions.

Continuous MonitorsContinuous Monitors• Misfire• Fuel System• Comprehensive Components

NonNon--Continuous MonitorsContinuous Monitors• EGR System• O2 Sensors• Catalyst• Evaporative System• Others (if vehicle equipped) –Secondary Air, Heated Catalyst,A/C System

System Monitors & Readiness Status

(Continued)

If a Monitor is run completely and the system / component being tested operates properly, the monitor is recorded in the powertrain control module (PCM) as ready, complete or done. Disconnecting the vehicles battery or clearing stored DTCs from the PCM will usually reset the monitor readiness status to NOT READY1996 – 2000 model year vehicles FAIL if more than 2 monitors are “Not Ready”.2001 and Newer model year vehicles FAIL if more than 1 monitor is “Not Ready”.

Drive CyclesWhat constitutes a DRIVE CYCLE can vary from monitor to monitor and across all makes and models.

Freeze FrameWhenever an emissions related malfunction

occurs, OBD II stores the operating parameters (conditions) present at the time

the malfunction occurs. Parameters recorded are, but are not limited to:

• Fuel Pressure• Fuel Trim Value ( Rich or Lean )• Engine Coolant Temperature• Intake Manifold Pressure• Open or Closed Loop Status

• This data is valuable to assist technicians in diagnosing the cause of the malfunction.

•DTC Description•Engine Speed•Vehicle Speed•Air Flow•Engine Load

System Reports

The TLC equipment will continue to produce reports as in the past.

Rejection Notices for vehicles failing an OBD II inspection will contain the following added information,Status of communication with PCMListing of DTC’s found storedNumber of monitors found “Not Ready”MIL status check

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

On board Diagnostics Regulations in the U.S.A. for On board Diagnostics Regulations in the U.S.A. for light and medium duty vehicles (internal combustion engines)light and medium duty vehicles (internal combustion engines)are introduced to implement the air quality standards.are introduced to implement the air quality standards.In this respect California Motor vehicle Pollution In this respect California Motor vehicle Pollution Control Board (CMVOCB) was created in 1960.Control Board (CMVOCB) was created in 1960.California and the federal government used a California and the federal government used a driving cycle to certify 1966 vehicles and newer driving cycle to certify 1966 vehicles and newer models which was referred to as either California models which was referred to as either California Cycle or the Federal Test Procedure (FTP) Cycle or the Federal Test Procedure (FTP) The following OBD II requirements are in force:The following OBD II requirements are in force:All vehicle’s emission control systems and components that can aAll vehicle’s emission control systems and components that can affect emissions must be ffect emissions must be monitored. Malfunctions must be detected before emissions exceedmonitored. Malfunctions must be detected before emissions exceed 1.5 times the standard 1.5 times the standard specified by EPA. specified by EPA. Malfunctions must be detected within 2 driving cycles.Malfunctions must be detected within 2 driving cycles.If a malfunction is detected a Malfunction Indicator Light (MIL)If a malfunction is detected a Malfunction Indicator Light (MIL) is illuminated.is illuminated.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

The First major Clean Air Act was adopted by the Congress in The First major Clean Air Act was adopted by the Congress in 1970. 1970. Congress established the Environmental Protection Agency Congress established the Environmental Protection Agency (EPA) with the overall responsibility of regulating motor (EPA) with the overall responsibility of regulating motor vehicle pollution to the atmosphere. Congress also identified vehicle pollution to the atmosphere. Congress also identified the Inspection and Maintenance (I/M) programs as an the Inspection and Maintenance (I/M) programs as an alternative for improving the air quality.alternative for improving the air quality.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

All of the previous regulations led to the appearance of the All of the previous regulations led to the appearance of the charcoal canister, exhaust gas recirculation (EGR) valves, and charcoal canister, exhaust gas recirculation (EGR) valves, and finally the catalytic converters in 1975.finally the catalytic converters in 1975.Moreover, in 1977 amendments to the Clean Air Act mandated Moreover, in 1977 amendments to the Clean Air Act mandated inspection and maintenance for vehicles used in highinspection and maintenance for vehicles used in high--pollution areas affected by high Hydro carbon (HC) emissions.pollution areas affected by high Hydro carbon (HC) emissions.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

On Board Diagnostics (OBD) systems were designed to On Board Diagnostics (OBD) systems were designed to maintain lowmaintain low--emissions of inemissions of in--use vehicles, includinguse vehicles, includinglight and medium duty vehicles.light and medium duty vehicles.

In 1989, The California Code of Regulations (CCR) known as In 1989, The California Code of Regulations (CCR) known as OBD II was adopted by the California Air Resources BoardOBD II was adopted by the California Air Resources Board(CARB) (CARB)

OBD II is the next generation OBD system of vehicles OBD II is the next generation OBD system of vehicles designed to reduce the time between occurrence of the designed to reduce the time between occurrence of the malfunction and its detection and repair, with the objective malfunction and its detection and repair, with the objective to reduce hydrocarbon (HC) emissions caused by to reduce hydrocarbon (HC) emissions caused by malfunction of the vehicle’s emission control system.malfunction of the vehicle’s emission control system.

Introduction to On Board Introduction to On Board Diagnostics (II) Diagnostics (II)

OBD II system is designed to satisfy EPA regulations whichOBD II system is designed to satisfy EPA regulations whichlimit the amount of HC emissions from the vehicle.limit the amount of HC emissions from the vehicle.

OBD II will also minimize the damage to other vehicle OBD II will also minimize the damage to other vehicle systems or components.systems or components.Such diagnostic systems are implemented by incorporating Such diagnostic systems are implemented by incorporating additional software and hardware in the vehicle electronicsadditional software and hardware in the vehicle electronicssystem to collect and analyze data already available to the system to collect and analyze data already available to the onon--board computer, and monitoring the entire emission control board computer, and monitoring the entire emission control system. system.

Introduction to On Board Introduction to On Board Diagnostics (II) Diagnostics (II)

The U.S. Federal Government has published test procedures that iThe U.S. Federal Government has published test procedures that include nclude several steps such as Dynamometer test, Hydro Carbons Analyzer,several steps such as Dynamometer test, Hydro Carbons Analyzer, and otherand otherAnalyzers. The vehicle is operated according to a prescribed schAnalyzers. The vehicle is operated according to a prescribed schedule of speed and load edule of speed and load to simulate highway driving as well city driving. The emissions to simulate highway driving as well city driving. The emissions are then measured using are then measured using the above instruments. Standards have been set for the vehicle the above instruments. Standards have been set for the vehicle halfhalf--life (5 years or 50000 life (5 years or 50000 miles which ever comes first) and full cycle (10 years or 1000miles which ever comes first) and full cycle (10 years or 100000 miles). The following 00 miles). The following standards are enforced 100% after 1996:standards are enforced 100% after 1996:

HC 0.31HC 0.31 gmsgms /mile/mileCO 4.20CO 4.20 gmsgms/mile/mileNOxNOx 0.600.60 gmsgms/mile (non/mile (non--diesel)diesel)

1.251.25 gmsgms/mile (diesel)/mile (diesel)

Introduction to On Board Introduction to On Board Diagnostics (II) Diagnostics (II)

These FTP regulations are enforced by EPA for all Light and These FTP regulations are enforced by EPA for all Light and Medium Duty vehicles made in U.S.A. The standards for Medium Duty vehicles made in U.S.A. The standards for European and Asian made vehicles have different standards European and Asian made vehicles have different standards which are more relaxed.which are more relaxed.The European andThe European and AseanAsean standards are not yet completely standards are not yet completely finalized by their countries.finalized by their countries.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

OBD II requires the manufacturers to implement new comprehensiveOBD II requires the manufacturers to implement new comprehensiveonon--board diagnostic systems beginning in the 1994 model year, board diagnostic systems beginning in the 1994 model year, to replace OBD Ito replace OBD I

The EPA in 1978 issued its first policy for Inspection and The EPA in 1978 issued its first policy for Inspection and Maintenance (I/M) of vehicles that emitted Hydro Carbons intoMaintenance (I/M) of vehicles that emitted Hydro Carbons intothe atmosphere.the atmosphere.

As emissions increased, the EPA regulations grew stricter, resulAs emissions increased, the EPA regulations grew stricter, resulting ting in the introduction of the 3in the introduction of the 3--way catalytic converter, onway catalytic converter, on--board computers board computers and oxygen sensors in 1981.and oxygen sensors in 1981.

OBD II monitors more components and systems OBD II monitors more components and systems than OBDthan OBD--I, including:I, including:

Catalytic convertersCatalytic convertersEvaporative control SystemEvaporative control SystemEmissions control systemEmissions control systemEmissions relatedEmissions related powertrainpowertrain performance performance -- Oxygen sensorOxygen sensorEmissions related sensors and actuatorsEmissions related sensors and actuators-- EGR monitoringEGR monitoringDetection of engine misfireDetection of engine misfirePCV (Positive Crankcase Ventilation) (implementation: 2002 PCV (Positive Crankcase Ventilation) (implementation: 2002 -- 2004)2004)Fuel system Fuel system -- closed loop fueling performanceclosed loop fueling performanceThermostats (implementation: 2000 Thermostats (implementation: 2000 -- 2002)2002)

Components are monitored for :Components are monitored for :uuCircuit continuity and out of range values of sensors, actuatorsCircuit continuity and out of range values of sensors, actuators, switches, and wires, switches, and wiresuuFunctional checks for output components listed aboveFunctional checks for output components listed aboveuuReasonable value checks during vehicle operation such as rationaReasonable value checks during vehicle operation such as rationality, sanity, or logic checks for lity, sanity, or logic checks for input components, and output components where applicable.input components, and output components where applicable.Thermostat monitoring is the new addition to the existing OBD IIThermostat monitoring is the new addition to the existing OBD II requirements. This is requirements. This is required due to:required due to:uuThermostat degradation can extend the time of openThermostat degradation can extend the time of open--loop operation at startloop operation at start--upupuuProlonged openProlonged open--loop operation will increase emissionsloop operation will increase emissionsuu“warmed“warmed--up” coolant temperature is a must for all OBD II monitoring operup” coolant temperature is a must for all OBD II monitoring operations.ations.New requirements for thermostats for 2000New requirements for thermostats for 2000--2002 implementation include the following:2002 implementation include the following:uuDetection of malfunctions that will affect the coolant temperatuDetection of malfunctions that will affect the coolant temperature and disable OBD II monitoring functions due to lower than re and disable OBD II monitoring functions due to lower than normal temperature operation of the vehiclenormal temperature operation of the vehicleuuDetection of malfunctions that will prevent vehicle from reachinDetection of malfunctions that will prevent vehicle from reaching normal operating temperature.g normal operating temperature.

PCV (Positive Crankcase Ventilation) failure will increase the ePCV (Positive Crankcase Ventilation) failure will increase the emissions by 1.2 g/mi for Hydro Carbons per vehiclemissions by 1.2 g/mi for Hydro Carbons per vehiclePCV must be monitored for this reason and its requirements are:PCV must be monitored for this reason and its requirements are:Detect PCV hose disconnections that can cause increased emissionDetect PCV hose disconnections that can cause increased emissionssMeet all design guidelines concerning hoses and valve connectionMeet all design guidelines concerning hoses and valve connections and materials to ensures and materials to ensurepositive crankcase ventilation. positive crankcase ventilation.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

The intent of OBD II systems is to detect most vehicleThe intent of OBD II systems is to detect most vehiclemalfunctions when performance of amalfunctions when performance of a powertrainpowertrain component or component or system deteriorates to the point thatsystem deteriorates to the point thatthe vehicle’s HC emissions exceed the thresholdthe vehicle’s HC emissions exceed the thresholdvalue tied to the applicable EPA emission standard. value tied to the applicable EPA emission standard. The vehicle operator is notified at the time when the vehicle The vehicle operator is notified at the time when the vehicle begins to marginally exceed emission standards, by begins to marginally exceed emission standards, by illuminating the Malfunction Indicator Light (MIL) illuminating the Malfunction Indicator Light (MIL)

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

Both CARB and EPA regulations require monitoring of systems, andBoth CARB and EPA regulations require monitoring of systems, and illuminating illuminating MIL and storage of a Diagnostic Trouble Code (DTC) if a fault iMIL and storage of a Diagnostic Trouble Code (DTC) if a fault is detected.s detected.Once per trip evaluation:Once per trip evaluation:uuCatalyst efficiency (conversion efficiency)Catalyst efficiency (conversion efficiency)uuHeated catalyst (time to attain rated temperature)Heated catalyst (time to attain rated temperature)uuEvaporative system (air flow /vapor leak detection) Evaporative system (air flow /vapor leak detection) uuSecondary Air system (proper air amount during idle)Secondary Air system (proper air amount during idle)uuOxygen sensor (output voltage and response frequency)Oxygen sensor (output voltage and response frequency)uuOxygen sensor heater (proper current and voltage drop)Oxygen sensor heater (proper current and voltage drop)uuEGR system (proper exhaust gas flow rate into intake manifold)EGR system (proper exhaust gas flow rate into intake manifold)

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

Continuous evaluation:Continuous evaluation:uuMisfire detection (percent misfire and specific cylinder Misfire detection (percent misfire and specific cylinder number)number)uuFuel system performance (proper fuel delivery and nozzle Fuel system performance (proper fuel delivery and nozzle flow)flow)uuComprehensive component monitoring Comprehensive component monitoring -- Input sensor and Input sensor and output actuator that can affect emissions.output actuator that can affect emissions.uuincrease in emissions greater than 50 % of standard is increase in emissions greater than 50 % of standard is considered objectionable.considered objectionable.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

OBD II is an onboard diagnostics and service methodology.OBD II is an onboard diagnostics and service methodology.OBD II mandates a standard scan tool (SAE J 1978) with a singleOBD II mandates a standard scan tool (SAE J 1978) with a single standardstandardplug for all vehicles manufactured in U.S.A.plug for all vehicles manufactured in U.S.A.Diagnostic test modes (SAE J 1979) include:Diagnostic test modes (SAE J 1979) include:uuFault code handling Fault code handling uu“Readiness” codes “Readiness” codes uuReal time vehicle informationReal time vehicle informationuu“Freeze Frame” information.“Freeze Frame” information.

Standard nomenclature for all OBD II codes (SAE J 1930) is mandaStandard nomenclature for all OBD II codes (SAE J 1930) is mandated.ted.

OBD II standardizes on most Trouble Codes (TC) for vehicleOBD II standardizes on most Trouble Codes (TC) for vehiclemalfunctions identified by regions, such asmalfunctions identified by regions, such as powertrainpowertrain, body, etc., body, etc.OBD II standardizes on number of sensor readings, messageOBD II standardizes on number of sensor readings, messageformats, message priorities, etc. for all vehicles.formats, message priorities, etc. for all vehicles.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

OBD II standardizes on the amount of memory (“Freeze OBD II standardizes on the amount of memory (“Freeze Frame”) it uses to store the readings of the vehicle sensors wheFrame”) it uses to store the readings of the vehicle sensors when n it logs an emission related intermittent (“history”) Trouble it logs an emission related intermittent (“history”) Trouble Code(TC).Code(TC).

OBD II standardizes on diagnostic method of storing trouble OBD II standardizes on diagnostic method of storing trouble codes and displaying Malfunction Indicator Light (MIL) which codes and displaying Malfunction Indicator Light (MIL) which cannot be removed until the malfunction is repaired.cannot be removed until the malfunction is repaired.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

OBD II provides additional information to technician for diagnosOBD II provides additional information to technician for diagnosis and repair is and repair of emission related problems.of emission related problems.

Item Legal Requirement Diagnostic tItem Legal Requirement Diagnostic techniqueechnique____________________________________________________________________________________________________________

Catalytic Converter Illuminate MIL Catalytic Converter Illuminate MIL Dual sensors placedDual sensors placedmonitoring when HC conversion efficiency monitoring when HC conversion efficiency at the front and rear end of the at the front and rear end of the

falls to 60% falls to 60% converterconverter______________________________________________________________________________________________________________________________________________________Misfire monitoring Illuminate MIL on detecting Misfire monitoring Illuminate MIL on detecting Measure change in Measure change in

misfires in predefinmisfires in predefined % of crankshaft speeded % of crankshaft speedmisfires in any cylinmisfires in any cylinder(s) and estimate indicatedder(s) and estimate indicatedwithin 200 or 1000 rewithin 200 or 1000 revolutions torque developed by volutions torque developed by

depending on cold start depending on cold start each cylinder aftereach cylinder after(open(open--loop) or loop) or combustion.combustion.closedclosed--loop operation. loop operation.

Complicated computationsComplicated computationsare carried out. Also iare carried out. Also identify dentify

the specific cylinder expethe specific cylinder experiencing riencing misfire.misfire.

______________________________________________________________________________________________________________________________________________________________

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

______________________________________________________________________________________________________________________________________________________________

Fuel System Illuminate MIL when deviations, ofFuel System Illuminate MIL when deviations, of Measure Measure deviations of fuel demanddeviations of fuel demandmonitoringmonitoring stoichiometricstoichiometric ratio which last for a fromratio which last for a fromstoichiometricstoichiometric ratio over ratio over

longer time stored within longer time stored within adaptive prolonged adaptive prolonged amount of time. Compareamount of time. Compare

mixture controller, exceedmixture controller, exceed defined value of Lambda defined value of Lambda sensor with Osensor with O2 2 sensorsensor

limits due to fuel system limits due to fuel system components not complyingcomponents not complyingwith specification. with specification.

______________________________________________________________________________________________________________________________________________________________

________________________________________________________________________________________________________________________________________________________________Oxygen sensor Illuminate MIL when the switching Oxygen sensor Illuminate MIL when the switching Monitor response time of two lambdaMonitor response time of two lambdamonitoring frequency of the controlmonitoring frequency of the control--loop exceeds sensors in front and rear of theloop exceeds sensors in front and rear of the

predefined limit. Check inpupredefined limit. Check input circuit catalytic converter. Lambda sensor t circuit catalytic converter. Lambda sensor voltage for detecting short voltage for detecting short circuit reacts slower on variations of the A/Fcircuit reacts slower on variations of the A/For open circuit. Bias is 0.45or open circuit. Bias is 0.450 volts. mixture, thus increasing the period of 0 volts. mixture, thus increasing the period of

the lambda sensor reguthe lambda sensor regulation which lation which is the inverse of the is the inverse of the closedclosed--looploopfrequency.frequency.

________________________________________________________________________________________________________________________________________________________________________EGR monitoring Illuminate MIL when EGR operation EGR monitoring Illuminate MIL when EGR operation Monitor manifold temperature change,Monitor manifold temperature change,

fails to indicate increase fails to indicate increase manifold pressure change, on EGR flomanifold pressure change, on EGR flow andw andin Manifold pressure or in Manifold pressure or engine RPM change as well. Use sensorsengine RPM change as well. Use sensorsfails to indicate increase fails to indicate increase in to detect these changes.in to detect these changes.manifold intake temperaturemanifold intake temperature or . or . decrease of about 50 enginedecrease of about 50 engine RPM.RPM.

EGR can be intrusively induceEGR can be intrusively induced duringd duringnormal operation, or interrupnormal operation, or interruptedtedwhen EGR operation is occurrwhen EGR operation is occurring and ing and monitor these changes.monitor these changes.

______________________________________________________________________________________________________________________________________________________Secondary Air Illuminate MIL when lambda sensor Secondary Air Illuminate MIL when lambda sensor Monitor lambda sensor reading whenMonitor lambda sensor reading whensystem monitoring deviation does not correlate with system monitoring deviation does not correlate with secondary air is introduced into the secondary air is introduced into the

secondary air flow changessecondary air flow changes. exhaust manifold or catalytic. exhaust manifold or catalyticIn openIn open--loop operation, the air flow converter’s secondloop operation, the air flow converter’s second chamber.chamber.should be into exhaust mashould be into exhaust manifoldnifoldprovided manifold temperatprovided manifold temperature isure isbelow threshold and enginebelow threshold and engine load isload isbelow threshold. In closebelow threshold. In closedd--looploopoperation the air flow shoperation the air flow should beould beinto catalytic converter’into catalytic converter’s seconds secondchamber in threechamber in three--way catalytic converter.way catalytic converter.

______________________________________________________________________________________________________________________________________________________________

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

Most components are monitored, including the catalyst and Most components are monitored, including the catalyst and evaporative system, such that a malfunction is signaled as the evaporative system, such that a malfunction is signaled as the emissions exceed 1.5 time the applicable standards.emissions exceed 1.5 time the applicable standards.

OBD II requires the detection of relatively low rates of engine OBD II requires the detection of relatively low rates of engine misfire, to prevent serious damage to the catalytic converter .misfire, to prevent serious damage to the catalytic converter .

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

Further, OBD II also includes “Freeze Frame”, which allows the Further, OBD II also includes “Freeze Frame”, which allows the computer to store in memory the exact operating conditions computer to store in memory the exact operating conditions when a fault occurred, so intermittent faults can be investigatewhen a fault occurred, so intermittent faults can be investigated d by revisiting the same conditions when the problem occurred.by revisiting the same conditions when the problem occurred.

A standard access electrical connector which is identical for alA standard access electrical connector which is identical for all l vehicles is required, which means that a single inexpensive vehicles is required, which means that a single inexpensive generic tool can be used to read out fault codes.generic tool can be used to read out fault codes.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

Although OBD II requirements reflect stateAlthough OBD II requirements reflect state--ofof--thethe--art diagnostic art diagnostic system capability, there are limitations which apply to the system capability, there are limitations which apply to the current techniques for detecting malfunctioning components. current techniques for detecting malfunctioning components. These limitations do not allow OBD II systems to take the place These limitations do not allow OBD II systems to take the place of the FTP test for measuring vehicle emissions.of the FTP test for measuring vehicle emissions.

The reason is that monitoring systems can detect when The reason is that monitoring systems can detect when components are functioning within their operating range, but components are functioning within their operating range, but are limited with the ability to determine whether they are are limited with the ability to determine whether they are functioning accurately within the range. functioning accurately within the range.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

OBD II is associated with IM240, the enhanced inspection/maintenOBD II is associated with IM240, the enhanced inspection/maintenance ance program for states with air quality program like California.program for states with air quality program like California.

IM240 also gets into the area of the new ASE (Automotive IM240 also gets into the area of the new ASE (Automotive Service Engineering) tests for the “super mechanics.”Service Engineering) tests for the “super mechanics.”

OBD II rules are copied from the CARB rules until 1997.OBD II rules are copied from the CARB rules until 1997.OBD II rules for 1998 will be taken from EPA’s standards which iOBD II rules for 1998 will be taken from EPA’s standards which includencludeamong other things, an onboard computer to predict when a vehicamong other things, an onboard computer to predict when a vehicle le will fail an emission test. will fail an emission test.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

OBD II standardizes that many trouble codes which are set whenOBD II standardizes that many trouble codes which are set whena malfunction is detected in the emission related component of ta malfunction is detected in the emission related component of the he vehicle will be stored in computer memory without a prospect vehicle will be stored in computer memory without a prospect for erasure prior to repair.for erasure prior to repair.OBD II mandates that all trouble codes are logged when theyOBD II mandates that all trouble codes are logged when theyare set and are retrieved by the scan tool when commanded.are set and are retrieved by the scan tool when commanded.OBD II however turns on the Malfunction Indictor Light (MIL)OBD II however turns on the Malfunction Indictor Light (MIL)selectively in malfunction situations that require immediate selectively in malfunction situations that require immediate attention of the driver for safety reasons. attention of the driver for safety reasons.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

Specific “Freeze Frame” diagnostic data must be stored when Specific “Freeze Frame” diagnostic data must be stored when the first malfunction is detected. If a second malfunction in ththe first malfunction is detected. If a second malfunction in the e fuel system or misfire function occurs, then the first data mustfuel system or misfire function occurs, then the first data mustbe replaced with the subsequent malfunction data. Diagnostic be replaced with the subsequent malfunction data. Diagnostic data must be made available when requested by the Scan tool. data must be made available when requested by the Scan tool. Results of the most recent tests and limits to which those resulResults of the most recent tests and limits to which those results ts are compared with, must be made available for all emission are compared with, must be made available for all emission control systems, for which OBD II diagnostics are conducted. control systems, for which OBD II diagnostics are conducted. The message content and down loading protocol is defined for The message content and down loading protocol is defined for all fault codes, specific data values, and “Freeze Frame” data.all fault codes, specific data values, and “Freeze Frame” data.

Introduction to On Board Introduction to On Board Diagnostics (II)Diagnostics (II)

Malfunction must be detected before emissions exceed a specifiedMalfunction must be detected before emissions exceed a specified threshold threshold (generally 1.5 times the standards). In most cases, malfunctions(generally 1.5 times the standards). In most cases, malfunctions must be must be detected and logged within two (2) driving Cycles (California Cydetected and logged within two (2) driving Cycles (California Cycles) or cles) or trips. trips.

R & D(research and development) activity in monitoring malfunctiR & D(research and development) activity in monitoring malfunctions of ons of vehicle components such as catalytic converters continues at avehicle components such as catalytic converters continues at a very rapid very rapid pace. pace.

There is plenty of room for the application of advanced control There is plenty of room for the application of advanced control and signal and signal processing techniques to control vehicle exhaust emissions usinprocessing techniques to control vehicle exhaust emissions using OBD II. g OBD II.

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger VehiclesVehicles

An Overview:An Overview:OnOn--line diagnosis of internal combustion engines in passenger vehicline diagnosis of internal combustion engines in passenger vehicleslesis mandated due to the strict environmental regulations in the Uis mandated due to the strict environmental regulations in the U.S.A .S.A and in some European countries (e.g.., the EFTA (European Free Tand in some European countries (e.g.., the EFTA (European Free TraderadeAgency) partners) to control Hydro carbon emissions from the exhAgency) partners) to control Hydro carbon emissions from the exhaust.aust.

PowertrainPowertrain subsystem consists of the engine and transmission including thesubsystem consists of the engine and transmission including theexhaust emission control apparatus which needs to be continuouslexhaust emission control apparatus which needs to be continuously y monitored by the engine controller (computer) for potential defemonitored by the engine controller (computer) for potential defects cts leading to decreased effectiveness in emission control system (eleading to decreased effectiveness in emission control system (e.g., three.g., three--waywaycatalyst) resulting in increased emission of hydrocarbons which catalyst) resulting in increased emission of hydrocarbons which are regulated are regulated by the EPA.by the EPA.

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))

TheThe powertrainpowertrain components relevant to emissions are:components relevant to emissions are:Throttle & ManifoldThrottle & ManifoldExhaust & Fuel systemExhaust & Fuel systemCombustion & Rotational dynamicsCombustion & Rotational dynamicsAutomatic TransmissionAutomatic Transmission

Each of the above components is further divided into the followiEach of the above components is further divided into the following subng sub--components:components:

Throttle & manifold: Throttle & manifold: Throttle Body assemblyThrottle Body assemblyIdle Air Control Valve (IACV)Idle Air Control Valve (IACV)Exhaust Gas Recirculation (EGR)Exhaust Gas Recirculation (EGR)Intake ManifoldIntake Manifold

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))

Exhaust & Fuel system consists of the following components: Exhaust & Fuel system consists of the following components: Exhaust & Fuel system:Exhaust & Fuel system:

Exhaust valvesExhaust valvesExhaust Gas lineExhaust Gas lineFuel PumpFuel PumpFuel Level SensorFuel Level SensorVacuum SensorVacuum SensorCanister VentCanister VentFuel Feed and MeteringFuel Feed and MeteringFuel Injection nozzlesFuel Injection nozzlesOxygen sensorOxygen sensorCatalytic ConverterCatalytic Converter

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))

Combustion and Rotational dynamics consist of the following compCombustion and Rotational dynamics consist of the following components:onents:Combustion and Rotational dynamics:Combustion and Rotational dynamics:

EngineEngineCrankshaft assembly and flywheelCrankshaft assembly and flywheelCrank angle sensorCrank angle sensorMass Air Flow (MAF) sensorMass Air Flow (MAF) sensorCoolant Temperature sensorCoolant Temperature sensorManifold Absolute Pressure (MAP) sensorManifold Absolute Pressure (MAP) sensorEngine Speed sensorEngine Speed sensorKnock sensorKnock sensorpurge solenoidpurge solenoid

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))

Automatic transmission consists of the following components:Automatic transmission consists of the following components:Automatic Transmission:Automatic Transmission:

Torque ConverterTorque ConverterAutomatic transmission input shaftAutomatic transmission input shaftTransmission lockup clutchTransmission lockup clutchHydraulic pump and hydraulic circuitHydraulic pump and hydraulic circuitSolenoid valvesSolenoid valvesThrottle Position sensorThrottle Position sensorVehicle Speed sensorVehicle Speed sensorTransmission input shaft speed sensorTransmission input shaft speed sensor

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))

The goal of the OnThe goal of the On--Board Diagnostics is to alert the driver to the presence of Board Diagnostics is to alert the driver to the presence of a malfunction of the emission control system , and to identify ta malfunction of the emission control system , and to identify the location of he location of the problem in order to assist mechanics in properly performing the problem in order to assist mechanics in properly performing repairs. In repairs. In addition, the OBD II system should illuminate the Malfunction Inaddition, the OBD II system should illuminate the Malfunction Indicator dicator Light (MIL) and store the Trouble Code in the computer memory foLight (MIL) and store the Trouble Code in the computer memory for all r all malfunctions that will contribute to increased HC emissions.malfunctions that will contribute to increased HC emissions.

TheThe PowertrainPowertrain is controlled by theis controlled by the PowertrainPowertrain control module (PCM) control module (PCM) computer to deliver the required torque to the vehicle requestedcomputer to deliver the required torque to the vehicle requested by the by the driver and to limit the vehicle emissions to the required minimudriver and to limit the vehicle emissions to the required minimum to meet m to meet EPA regulations. EPA regulations.

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))

TheThe powertrainpowertrain functions are described to show how the PCM controls the emissifunctions are described to show how the PCM controls the emissions while delivering the ons while delivering the torque to the vehicle requested by the driver.torque to the vehicle requested by the driver.Throttle & Intake Manifold: The Throttle Body assembly is an airThrottle & Intake Manifold: The Throttle Body assembly is an air valve. It regulates the air flow into thevalve. It regulates the air flow into theengine and thereby contributes to the control of engine speed anengine and thereby contributes to the control of engine speed and power. IACV d power. IACV (idle air control valve )provides additional air flow during st(idle air control valve )provides additional air flow during starting of the engine and during idle. arting of the engine and during idle. IACV bypasses the throttle to provide additional air to compensIACV bypasses the throttle to provide additional air to compensate for the loads during closed ate for the loads during closed throttle. EGR (exhaust gas recirculation)provides exhaust gasesthrottle. EGR (exhaust gas recirculation)provides exhaust gases to the intake manifold. This has the effect of to the intake manifold. This has the effect of reducing oxygen content in the enginereducing oxygen content in the enginecylinder. This in turn reduces the combustion temperature of thecylinder. This in turn reduces the combustion temperature of the cylinder flame. This has the cylinder flame. This has the important effect of reducing theimportant effect of reducing the NOxNOx (Oxides of nitrogen) emissions which is regulated by the EPA. (Oxides of nitrogen) emissions which is regulated by the EPA. Intake manifold is the main air passage from the throttle valve Intake manifold is the main air passage from the throttle valve to the engine cylinders. The amount to the engine cylinders. The amount of air through the intake manifold to the cylinder is the same fof air through the intake manifold to the cylinder is the same for each cylinder on each intake stroke.or each cylinder on each intake stroke.Then each cylinder requires an amount of fuel determined by the Then each cylinder requires an amount of fuel determined by the density of the air in the cylinder. density of the air in the cylinder. MAP sensor is used to compute the density of the air in the intaMAP sensor is used to compute the density of the air in the intake manifold. Barometric absoluteke manifold. Barometric absolutepressure is used to compute the EGR flow. The Manifold vacuum ispressure is used to compute the EGR flow. The Manifold vacuum is the difference between these the difference between these two pressures which is measured. The required fuel is in direct two pressures which is measured. The required fuel is in direct proportion to this air mass which proportion to this air mass which is controlled by the PCM to maintain the exactis controlled by the PCM to maintain the exact stoichiometricstoichiometric ratio (14.7) of air/fuel that gives theratio (14.7) of air/fuel that gives theminimum HC emissions and meet EPA regulations. minimum HC emissions and meet EPA regulations.

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))

Exhaust & Fuel system: Exhaust & Fuel system: Exhaust valves of the engine cylinders purge the exhaust throughExhaust valves of the engine cylinders purge the exhaust through the Exhaust Gas linethe Exhaust Gas linewhich then passes through the catalytic converters in which mostwhich then passes through the catalytic converters in which most of the HC and CO (carbonof the HC and CO (carbonmonoxide) are oxidized to COmonoxide) are oxidized to CO2 2 (Carbon dioxide) and water. The extra oxygen required for this(Carbon dioxide) and water. The extra oxygen required for thisoxidation is supplied by adding air to the exhaust stream from oxidation is supplied by adding air to the exhaust stream from an engine driven air pump. This airan engine driven air pump. This aircalled secondary air, is normally introduced into the exhaust mcalled secondary air, is normally introduced into the exhaust manifold. This has a considerableanifold. This has a considerable

effect in reducing emissions and meet EPA regulations.effect in reducing emissions and meet EPA regulations.The Fuel Pump supplies metered fuel which is electronically injeThe Fuel Pump supplies metered fuel which is electronically injected through nozzles operated cted through nozzles operated by solenoids under control of the PCM. The fuel in the fuel tankby solenoids under control of the PCM. The fuel in the fuel tank is filtered. is filtered. The Fuel Level Sensor measures the amount of fuel in the tank. The Fuel Level Sensor measures the amount of fuel in the tank. The vacuum sensor measures the inlet vacuum which is a measure oThe vacuum sensor measures the inlet vacuum which is a measure of fuel pump suction which f fuel pump suction which affects pump priming. The inlet vacuum is monitored to ensure thaffects pump priming. The inlet vacuum is monitored to ensure that inlet flow of the fuel to theat inlet flow of the fuel to thecylinders is not restricted. cylinders is not restricted.

PowertrainPowertrain and Emission and Emission Control in Passenger Vehicles Control in Passenger Vehicles ((contdcontd))

Canister vent & Fuel systemThe Canister Vent is used to direct fuel vapors out to a canisteThe Canister Vent is used to direct fuel vapors out to a canister where the vapors are r where the vapors are

absorbed by active char coal in the canister. The purge of the fabsorbed by active char coal in the canister. The purge of the fuel vapors is done uel vapors is done via purge valve periodically. via purge valve periodically.

The Fuel Feed and Metering is performed, by the PCM, to match thThe Fuel Feed and Metering is performed, by the PCM, to match the mass air flow e mass air flow which minimizes HC emissions. The air flow is controlled by the which minimizes HC emissions. The air flow is controlled by the throttle valve throttle valve which is operated by the driver’s pedal. which is operated by the driver’s pedal.

The Fuel Injection nozzles inject the fuel as a spray that spreThe Fuel Injection nozzles inject the fuel as a spray that spreads the fuel into the ads the fuel into the cylinder in an atomized manner to mix with the air for complete cylinder in an atomized manner to mix with the air for complete combustion. combustion.

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))Oxygen sensor:

The Oxygen sensor is used to monitor the residual oxygen (afterThe Oxygen sensor is used to monitor the residual oxygen (after catalysis in the catalysis in the converter) in the exhaust gases. The oxygen sensor output is caconverter) in the exhaust gases. The oxygen sensor output is calibrated to librated to measure the air/fuel ratio (which is proportional to oxygen in tmeasure the air/fuel ratio (which is proportional to oxygen in the exhaust gases) he exhaust gases) in the engine cylinders. This ratio, called Lambda, is one (1) in the engine cylinders. This ratio, called Lambda, is one (1) forfor stoichiometricstoichiometric(14.7) air/fuel ratio. This is the target for realizing minimum(14.7) air/fuel ratio. This is the target for realizing minimum emissions. emissions.

The oxygen sensor is used asThe oxygen sensor is used as stoichiometrystoichiometry detector and is connected in a closed detector and is connected in a closed loop in a Limit Cycle control. The oxygen sensor output is a swiloop in a Limit Cycle control. The oxygen sensor output is a switch signal tch signal (ON/OFF) that brings back the A/F ratio to 1 when it varies betw(ON/OFF) that brings back the A/F ratio to 1 when it varies between 0.93 to 1.07.een 0.93 to 1.07.

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))

The reason that oxygen sensor behaves in this manner is that The reason that oxygen sensor behaves in this manner is that the catalytic converter is most efficient in eliminating all the catalytic converter is most efficient in eliminating all pollutants by oxidizing HC to COpollutants by oxidizing HC to CO22 and reducingand reducing NOxNOx to Nto N22when the exhaust gases indicate awhen the exhaust gases indicate a stoichiometricstoichiometric (14.7) air/fuel (14.7) air/fuel ratio, indicated by the Exhaust Gas Oxygen (EGO) Sensor..ratio, indicated by the Exhaust Gas Oxygen (EGO) Sensor..Catalytic Converter is a three way catalyst which will oxidize Catalytic Converter is a three way catalyst which will oxidize the Hydro carbons including CO to COthe Hydro carbons including CO to CO22 and reduce theand reduce the NOx NOx to to NN22 in the exhaust gases simultaneously thus removing in the exhaust gases simultaneously thus removing pollutants.

Oxygen sensor

pollutants.

Combustion and Rotational dynamics: (Figures 1 to 3)Combustion and Rotational dynamics: (Figures 1 to 3)The Engine provides the mechanical power to the vehicle. The enThe Engine provides the mechanical power to the vehicle. The engine cylinders perform the combustion of air/fuel gine cylinders perform the combustion of air/fuel mixture atmixture at stoichiometricstoichiometric ratio (14.7). The Crankshaft assembly and flywheel house the Crratio (14.7). The Crankshaft assembly and flywheel house the Crank angle sensor which senses ank angle sensor which senses the position of the Top Dead center (TDC) of the cylinder and prthe position of the Top Dead center (TDC) of the cylinder and provides the necessary ignition spark at the correct crank ovides the necessary ignition spark at the correct crank angle between the reference point on the flywheel and the horizoangle between the reference point on the flywheel and the horizontal centerline of crank shaft. The amount of fuel needed ntal centerline of crank shaft. The amount of fuel needed for the combustion in the engine cylinder is a direct function ofor the combustion in the engine cylinder is a direct function of the throttle position and the mass of air through the intake f the throttle position and the mass of air through the intake manifold which is controlled by the driver’s accelerator pedal. manifold which is controlled by the driver’s accelerator pedal. This mass of air is measured with the Mass Air Flow This mass of air is measured with the Mass Air Flow (MAF) sensor. The correct air mass is computed by compensating f(MAF) sensor. The correct air mass is computed by compensating for the intake air temperature which is measured by the or the intake air temperature which is measured by the intake air temperature sensor. The Manifold Absolute Pressure (Mintake air temperature sensor. The Manifold Absolute Pressure (MAP) sensor measures the intake manifold pressure AP) sensor measures the intake manifold pressure which is also used to measure the amount of air going into the which is also used to measure the amount of air going into the cylinder as a second method to determine the amount of cylinder as a second method to determine the amount of fuel that should be sent to the fuel injection nozzles for sprayfuel that should be sent to the fuel injection nozzles for spraying into the cylinder. This is to ensure that accurate amount ing into the cylinder. This is to ensure that accurate amount of fuel is used in the cylinder to achieve fuel economy as wellof fuel is used in the cylinder to achieve fuel economy as well as to reduce emissions by efficient combustion. An Engine as to reduce emissions by efficient combustion. An Engine Speed sensor is needed to provide an input to PCM to compute igSpeed sensor is needed to provide an input to PCM to compute ignition timing. Engine speed is measured by engine nition timing. Engine speed is measured by engine speed sensor similar to crankshaft position sensor. Another varispeed sensor similar to crankshaft position sensor. Another variable which must be measured for engine control is the able which must be measured for engine control is the throttle angle or the throttle valve position which is measured throttle angle or the throttle valve position which is measured by the Throttle Angle Sensor.by the Throttle Angle Sensor.The throttle plate is mechanically linked to the accelerator pedThe throttle plate is mechanically linked to the accelerator pedal which is operated by the driver. When the pedal is al which is operated by the driver. When the pedal is pressed the throttle plate rotates and allows more air to pass tpressed the throttle plate rotates and allows more air to pass through the intake manifold. The angle of rotation of throttle hrough the intake manifold. The angle of rotation of throttle plate is measured by the throttle angle sensor. This can be usedplate is measured by the throttle angle sensor. This can be used to measure the mass of air going into the cylinder. to measure the mass of air going into the cylinder. Knock is caused by a rapid rise in cylinder pressure during combKnock is caused by a rapid rise in cylinder pressure during combustion caused by high manifold pressure (MAP) and ustion caused by high manifold pressure (MAP) and excessive spark advance. It is important to detect knock and avoexcessive spark advance. It is important to detect knock and avoid excessive knock to avoid damage to the engine. Knock id excessive knock to avoid damage to the engine. Knock is detected by the Knock sensor. is detected by the Knock sensor. During engine off condition, the fuel stored in the fuel system During engine off condition, the fuel stored in the fuel system tends to evaporate into tends to evaporate into the atmosphere. To reduce these HC emissions, they are collectedthe atmosphere. To reduce these HC emissions, they are collected by a charcoal filter in a canister. by a charcoal filter in a canister. The collected fuel is released into the fuel intake through a puThe collected fuel is released into the fuel intake through a purge solenoid valve controlled by therge solenoid valve controlled by thePCM periodically.PCM periodically.

PowertrainPowertrain and Emission and Emission Controls in Passenger Controls in Passenger Vehicles (Vehicles (contdcontd))

The Automatic transmission uses a hydraulic or fluid coupling toThe Automatic transmission uses a hydraulic or fluid coupling to transmit engine power to the wheels.transmit engine power to the wheels.Efficient transmission of engine output to the automatic transmiEfficient transmission of engine output to the automatic transmission input shaft is performed throughssion input shaft is performed througha transmission lockup clutch similar to a standard pressurea transmission lockup clutch similar to a standard pressure--plate clutch placed inside the torqueplate clutch placed inside the torqueconverter (the fluid coupling used as a torque amplifier). In orconverter (the fluid coupling used as a torque amplifier). In order to smoothly engage the lockup clutchder to smoothly engage the lockup clutchthe hydraulic fluid pressure is adjusted by controlling the outpthe hydraulic fluid pressure is adjusted by controlling the output current applied to the lockup solenoidut current applied to the lockup solenoidvalves. valves. Automatic transmission is controlled by inputs from the vehicle Automatic transmission is controlled by inputs from the vehicle speed sensor and throttle position sensorspeed sensor and throttle position sensorwhich senses the vehicle load. The automatic gear shift points, which senses the vehicle load. The automatic gear shift points, the point at which the lockupthe point at which the lockupclutch is activated, and the clutch’s hydraulic pressure level aclutch is activated, and the clutch’s hydraulic pressure level are controlled by the PCM. The optimalre controlled by the PCM. The optimalshifts and lockup operations are carried out using a solenoid vashifts and lockup operations are carried out using a solenoid valve to open and close the hydrauliclve to open and close the hydrauliccircuit, primed by the hydraulic pump. circuit, primed by the hydraulic pump. The transmission’s inputThe transmission’s input-- shaft speed is monitored during shifting by the speed sensor afshaft speed is monitored during shifting by the speed sensor after the ON/OFFter the ON/OFFsignal is output from the shift solenoid valves. The shifting psignal is output from the shift solenoid valves. The shifting process is adjusted by the hydraulic pressurerocess is adjusted by the hydraulic pressureof the clutch so that the clutch is smoothly engaged. The engineof the clutch so that the clutch is smoothly engaged. The engine torque is controlled in synchronism withtorque is controlled in synchronism withthe shift to reduce impact due to shift. During cruise, the locthe shift to reduce impact due to shift. During cruise, the lockup clutch is engaged and is disengagedkup clutch is engaged and is disengagedduring shifts, which improves fuel economy and emissions.during shifts, which improves fuel economy and emissions.

Automatic Automatic TransmissionTransmission::

OBD II for L & MD Vehicles OBD II for L & MD Vehicles STD ManualSTD Manual

OBD II Standards Manual:HSHS--3000 manual contains two sets of documents.3000 manual contains two sets of documents.

Diagnostics Committee documentsDiagnostics Committee documentsMultiplex Committee documents.Multiplex Committee documents.

The following standards are in the Diagnostics Committee documenThe following standards are in the Diagnostics Committee documents:ts:

SAE J 1930 Diagnostic Terms, Definitions, Abbreviations, and AcrSAE J 1930 Diagnostic Terms, Definitions, Abbreviations, and AcronymsonymsSAE J 1962 OBD II Diagnostic ConnectorSAE J 1962 OBD II Diagnostic ConnectorSAE J 1978 OBD II Scan ToolSAE J 1978 OBD II Scan ToolSAE J 1979 Diagnostics Test ModesSAE J 1979 Diagnostics Test ModesSAE J 2012 Trouble Code DefinitionsSAE J 2012 Trouble Code DefinitionsSAE J 2186 Data Link SecuritySAE J 2186 Data Link SecuritySAE J 2190 Enhanced E/E DiagnosticsSAE J 2190 Enhanced E/E Diagnostics Test ModesTest ModesSAE J 2201 Universal Interface for OBD II ScanSAE J 2201 Universal Interface for OBD II ScanSAE J 2205 Expanded Diagnostic Protocol For OBD II Scan ToolsSAE J 2205 Expanded Diagnostic Protocol For OBD II Scan Tools

The following standards are in the Multiplex Committee documentsThe following standards are in the Multiplex Committee documents::

SAE J 1850 Class B DATA Communications Network InterfaceSAE J 1850 Class B DATA Communications Network InterfaceSAE J 2178/1 Class B DATA SAE J 2178/1 Class B DATA CommunicationsCommunications Network Messages: Network Messages: Detailed Header Formats & Physical Address AssignmentsDetailed Header Formats & Physical Address AssignmentsSAE J 2178/2 Class B DATA Communications Network Messages : SAE J 2178/2 Class B DATA Communications Network Messages : Data Parameter DefinitionsData Parameter DefinitionsSAE J 2178/3 Class B DATA Communications Network Messages : SAE J 2178/3 Class B DATA Communications Network Messages : Frame IDs For Single Byte Forms OF HeadersFrame IDs For Single Byte Forms OF HeadersSAE J 2178/4 Class B DATA Communications Network Messages : SAE J 2178/4 Class B DATA Communications Network Messages : Message Definitions For Three Byte HeadersMessage Definitions For Three Byte Headers

OBD II for L & MD Vehicles OBD II for L & MD Vehicles STD ManualSTD Manual

OBD II has ten (10) major monitoring requirements: nine specifOBD II has ten (10) major monitoring requirements: nine specific monitors and one catch all. The ic monitors and one catch all. The nine monitors are: 1. Catalyst 2. Heated Catalyst 3. Misfire nine monitors are: 1. Catalyst 2. Heated Catalyst 3. Misfire 4. Evaporative system4. Evaporative system5. Secondary Air System 6. Air Conditioning System Refrigerant 5. Secondary Air System 6. Air Conditioning System Refrigerant (for CFC only) 7. Fuel system (for CFC only) 7. Fuel system 8. Oxygen Sensor 9. Exhaust Gas Recirculation (EGR) system. 10.8. Oxygen Sensor 9. Exhaust Gas Recirculation (EGR) system. 10. Comprehensive components Comprehensive components (sensors(sensors-- inputs & actuatorsinputs & actuators--outputs)outputs)The comprehensive components are mostly inputs and outputs to thThe comprehensive components are mostly inputs and outputs to thee powertrainpowertrain which are sensors, and which are sensors, and actuators. These have to be tested for circuit continuity, stucactuators. These have to be tested for circuit continuity, stuck at 1 and stuck at 0 (ground) faults,k at 1 and stuck at 0 (ground) faults,and for range/performance problems, andand for range/performance problems, and internittentinternittent faults.. faults.. OBD II has to communicate the diagnostic information to the vehiOBD II has to communicate the diagnostic information to the vehicle mechanic via a communicationcle mechanic via a communicationnetwork using diagnostic trouble codes (network using diagnostic trouble codes (DTCsDTCs). ). A special Connector , SAE J 1962, is used to facilitate the intA special Connector , SAE J 1962, is used to facilitate the interface for communication. erface for communication. The mechanic uses Scan Tool, SAE J 1978, to collect diagnosThe mechanic uses Scan Tool, SAE J 1978, to collect diagnostic messages from the vehicle. tic messages from the vehicle. The HSThe HS--3000 Manual specifies SAE standards for the above OBD II tools.3000 Manual specifies SAE standards for the above OBD II tools. Each SAE standard Each SAE standard specifies one particular component for compliance. The requiremespecifies one particular component for compliance. The requirements for each SAE standard are nts for each SAE standard are described below:described below:

OBD II for L & MD Vehicles OBD II for L & MD Vehicles STD ManualSTD Manual

OBD II diagnostics are required to comply with SAE standards liOBD II diagnostics are required to comply with SAE standards listed in the Hssted in the Hs--30003000manual. They relate to the following areas:manual. They relate to the following areas:SAE J 1930 defines the diagnostic terms applicable to electricalSAE J 1930 defines the diagnostic terms applicable to electrical/electronic systems, including /electronic systems, including mechanical terms, definitions, abbreviations, and acronyms. Thesmechanical terms, definitions, abbreviations, and acronyms. These terms only should be used by OBD II.e terms only should be used by OBD II.The standard will be continuously updated by SAE for compliance The standard will be continuously updated by SAE for compliance by OBD II in future.by OBD II in future.All documents related to emissionAll documents related to emission--related vehicle and engine service procedures shall conform to related vehicle and engine service procedures shall conform to the emission related the emission related nomenclature and abbreviations provided in SAE J 1930. This alsonomenclature and abbreviations provided in SAE J 1930. This also applies to all new documents printed or updated by a applies to all new documents printed or updated by a manufacturer starting 1993 model year.manufacturer starting 1993 model year.Common names for components and systems are recognized as benefiCommon names for components and systems are recognized as beneficial for technicians working on multiple models of cial for technicians working on multiple models of vehicles.vehicles. PowertrainPowertrain terms are approved in 1993. The standard is updated periodicallterms are approved in 1993. The standard is updated periodically by the task force.y by the task force.SAE J 1962 defines minimum set of diagnostic connector requiremSAE J 1962 defines minimum set of diagnostic connector requirements that all diagnostic toolsents that all diagnostic toolsmust satisfy to perform OBD II monitoring and diagnostic functimust satisfy to perform OBD II monitoring and diagnostic functions on board the vehicle. ons on board the vehicle. SAE J 1962 is a 16 pin connector located under the instrument paSAE J 1962 is a 16 pin connector located under the instrument panel on the driver side of the vehicle.nel on the driver side of the vehicle.The pin assignments are specified in the standard for SAE J 1850The pin assignments are specified in the standard for SAE J 1850 serial data link (2 pins), Battery power (pin 16), Battery grouserial data link (2 pins), Battery power (pin 16), Battery ground, nd, Signal Ground (pin 5), and ISO 9141 serial data link (2 pins). CSignal Ground (pin 5), and ISO 9141 serial data link (2 pins). Connector terminals 2,7,10, and 15 must be compatible with the onnector terminals 2,7,10, and 15 must be compatible with the assignment and use of their mating terminal in the vehicle connassignment and use of their mating terminal in the vehicle connector. Chassis ground is pin 4 and is defined in SAE J 2201. ector. Chassis ground is pin 4 and is defined in SAE J 2201. Battery ground must be noise free and a clean signal ground. TheBattery ground must be noise free and a clean signal ground. These are intended for compliance through out the motor vehicle se are intended for compliance through out the motor vehicle industry. The SAE standards are under the control and maintenancindustry. The SAE standards are under the control and maintenance of the Vehicle E/E System Diagnostics Committee. e of the Vehicle E/E System Diagnostics Committee.

OBD II for L & MD Vehicles OBD II for L & MD Vehicles STD ManualSTD Manual

The salient features of the SAE J 1962 standard that specifies tThe salient features of the SAE J 1962 standard that specifies the he OBDOBD II’sII’s diagnostic connector are:diagnostic connector are:Consistent location in the vehicle’s instrument Panel (IP), EaseConsistent location in the vehicle’s instrument Panel (IP), Easeof access to technician, Ease of Visibility to the technician, aof access to technician, Ease of Visibility to the technician, and nd Ease of attachment of equipment without affecting normal Ease of attachment of equipment without affecting normal vehicle operation.vehicle operation.The Connector design must be compatible with previous The Connector design must be compatible with previous vehicle configurations, must meet the electrical (10 A DC), and vehicle configurations, must meet the electrical (10 A DC), and mechanical specification of material, shape, mating mechanical specification of material, shape, mating requirements, and terminal assignments. requirements, and terminal assignments.

OBD II for L & MD Vehicles OBD II for L & MD Vehicles STD ManualSTD Manual

OBD II Scan Tool ( SAE J 1978 0):OBD II Scan Tool ( SAE J 1978 0):SAE J 1978 standard defines the requirements of the OBD II Scan SAE J 1978 standard defines the requirements of the OBD II Scan ToolTool. . This is an important function of OBD II. The Scan Tool must suppThis is an important function of OBD II. The Scan Tool must support the following OBD II functions:ort the following OBD II functions:1.Automatic hands1.Automatic hands--off determination of the communication interface used.off determination of the communication interface used.2. Obtaining and displaying the status and results of vehicle’s 2. Obtaining and displaying the status and results of vehicle’s onon--board diagnostic evaluations.board diagnostic evaluations.3. Obtaining and displaying OBD II emissions related diagnostic 3. Obtaining and displaying OBD II emissions related diagnostic trouble codes (trouble codes (DTCsDTCs).).4. Obtaining and displaying OBD II emissions related current dat4. Obtaining and displaying OBD II emissions related current data.a.5. Obtaining and displaying OBD II emissions related “freeze fra5. Obtaining and displaying OBD II emissions related “freeze frame” data.me” data.6. Clearing the storage of OBD II emissions related diagnostic t6. Clearing the storage of OBD II emissions related diagnostic trouble codes, OBD II emissionsrouble codes, OBD II emissionsrelated “freeze frame” data storage and OBD II emissions relatedrelated “freeze frame” data storage and OBD II emissions related diagnostic test status.diagnostic test status.7. Ability to perform Expanded Diagnostic protocol functions as 7. Ability to perform Expanded Diagnostic protocol functions as described in SAE J 2205.described in SAE J 2205.8. Obtaining and displaying OBD II emissions related test parame8. Obtaining and displaying OBD II emissions related test parameters and results as described in SAE J 1979.ters and results as described in SAE J 1979.9. Provide a user manual and/or help facility.9. Provide a user manual and/or help facility.

The Universal interface (SAE J 2201) requirements for Scan ToThe Universal interface (SAE J 2201) requirements for Scan Tool (SAE J 1978) , Data Communication ol (SAE J 1978) , Data Communication Network Interface (SAE J 1850) , (SAE J 1850) , Interface connecNetwork Interface (SAE J 1850) , (SAE J 1850) , Interface connector (SAE J 1962) requirements , Test Modes tor (SAE J 1962) requirements , Test Modes (SAE J 1979) , and Diagnostic Trouble codes (SAE J 2012), and (SAE J 1979) , and Diagnostic Trouble codes (SAE J 2012), and Enhanced test modes (SAE J 2190), are Enhanced test modes (SAE J 2190), are described in detail in the standard. General characteristics, eldescribed in detail in the standard. General characteristics, electrical and mechanical characteristics are also ectrical and mechanical characteristics are also described in the HSdescribed in the HS--3000 standard. EPA regulation is that SAE J 1978 must have the 3000 standard. EPA regulation is that SAE J 1978 must have the capability to perform bicapability to perform bi--directional diagnostic control. Vehicle manufacturers will use mdirectional diagnostic control. Vehicle manufacturers will use manufacturer specific messages to perform anufacturer specific messages to perform these functions, and later use SAE J 2205, (Expanded Scan Tool pthese functions, and later use SAE J 2205, (Expanded Scan Tool protocol) rotocol) to enable these functions with SAE J 1978 Scan tool.to enable these functions with SAE J 1978 Scan tool.

OBD II for L & MD Vehicles OBD II for L & MD Vehicles STD ManualSTD Manual

SAE 1979 defines the diagnostic test modes, and request and respSAE 1979 defines the diagnostic test modes, and request and response messages necessaryonse messages necessaryto be supported by the vehicle manufacturers and test tools to to be supported by the vehicle manufacturers and test tools to meet EPA related OBD II requirements.meet EPA related OBD II requirements.These messages are for use by the service tool capable of perfoThese messages are for use by the service tool capable of performing OBD II diagnostics.rming OBD II diagnostics.Diagnostic test modes from mode $01 to Mode $08 are described iDiagnostic test modes from mode $01 to Mode $08 are described in the standard. All test Modesn the standard. All test Modesexcept mode $ 08 are related to Request forexcept mode $ 08 are related to Request for Powertrain’s Powertrain’s emission related diagnostic data or test resultsemission related diagnostic data or test resultsor Diagnostic trouble Codes. Test Mode $ 08 is Request for Contror Diagnostic trouble Codes. Test Mode $ 08 is Request for Control of On Board system instead of theol of On Board system instead of thedata. All these requests are made by the Scan Tool SAE J 1978. data. All these requests are made by the Scan Tool SAE J 1978. Mode $01 is request currentMode $01 is request current powertrainpowertrain diagnostic data which are:diagnostic data which are:uuAnalog inputs and outputsAnalog inputs and outputsuuDigital inputs and outputsDigital inputs and outputsuuSystem status informationSystem status informationuucalculated valuescalculated valuesMode $ 02 is requestMode $ 02 is request powertrainpowertrain “Freeze Frame” data for the same items listed above“Freeze Frame” data for the same items listed aboveMode $03 is request emissionMode $03 is request emission--relatedrelated PowertrainPowertrain Diagnostic Trouble Codes (Diagnostic Trouble Codes (DTCsDTCs).).Mode $04 is Clear/Reset emission related diagnostic information.Mode $04 is Clear/Reset emission related diagnostic information.Mode $05 is request Oxygen sensor monitoring test results.Mode $05 is request Oxygen sensor monitoring test results.Mode $06 is request onMode $06 is request on--board monitoring test results for nonboard monitoring test results for non--continuously monitored systems.continuously monitored systems.Mode $07 is request onMode $07 is request on--board monitoring test results for continuously monitored systemsboard monitoring test results for continuously monitored systems..Mode $08 is request control of onMode $08 is request control of on--board system test, or component.board system test, or component.For each test mode this standard specifies:For each test mode this standard specifies:uuFunctional description of test mode.Functional description of test mode.uuRequest and response message formats.Request and response message formats.Examples of messages are included in the standard for explainingExamples of messages are included in the standard for explaining some complex test modes .some complex test modes .The diagnostic message format, response time (100 ms) and varioThe diagnostic message format, response time (100 ms) and various related data items are described in us related data items are described in detail in the standard. PID $1D in table for Mode $01 is added adetail in the standard. PID $1D in table for Mode $01 is added as alternate locations for Oxygen Sensor.s alternate locations for Oxygen Sensor.PID $1E in table for Mode $01 is added for Auxiliary input statPID $1E in table for Mode $01 is added for Auxiliary input status. There are 14 figures showing 14 tables describingus. There are 14 figures showing 14 tables describingPIDsPIDs, and messages for different Modes with their explanation includ, and messages for different Modes with their explanation including the method to determine if the data is valid.ing the method to determine if the data is valid.

Diagnostic Test Modes (SAE J 11979):

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Diagnostic Trouble Codes (SAE J 2012):

SAE J 2012 defines the Diagnostic Trouble Codes (SAE J 2012 defines the Diagnostic Trouble Codes (DTCsDTCs) for OBD II. This standard focuses on ) for OBD II. This standard focuses on diagnostic code format and code messages for automotive electrondiagnostic code format and code messages for automotive electronic control systems of all light andic control systems of all light andmedium duty vehicles. Themedium duty vehicles. The DTCsDTCs are defined by four basic categories. General Circuit Malfunctiare defined by four basic categories. General Circuit Malfunction,on,Range/Performance Problem, Low and High Circuit input. The DTC Range/Performance Problem, Low and High Circuit input. The DTC consists of an alphaconsists of an alpha--numericnumericdesignator, B0designator, B0--B3 for Body, C0B3 for Body, C0--C3 for Chassis, P0C3 for Chassis, P0--P3 forP3 for PowertrainPowertrain, and U0, and U0--U3 for Network U3 for Network Communication, followed by three digits. P0Communication, followed by three digits. P0--P3 forP3 for PowertrainPowertrain is OBDis OBD II’sII’s main concern.main concern.Diagnostic Trouble Codes are defined to indicate a suspected troDiagnostic Trouble Codes are defined to indicate a suspected trouble or problem area as a directive to the proper service uble or problem area as a directive to the proper service procedure. The DTC is intended to indicate only a malfunction neprocedure. The DTC is intended to indicate only a malfunction needing service and not when vehicle functions are normal. eding service and not when vehicle functions are normal. The decision to illuminate the MIL (Malfunction Indicator Light)The decision to illuminate the MIL (Malfunction Indicator Light) for any DTC is based on how the system malfunctionfor any DTC is based on how the system malfunctionaffects emissions.affects emissions.The standard has DTC code groupings designated as SAE ControlledThe standard has DTC code groupings designated as SAE Controlled, Manufacturer Controlled, and, Manufacturer Controlled, andreserved for future use. This prevents any manufacturer to changreserved for future use. This prevents any manufacturer to change any SAE Controllede any SAE Controlled DTCsDTCs and SAE toand SAE tochange Manufacturer’schange Manufacturer’s DTCsDTCs. . Each defined fault code is assigned a message to indicate the ciEach defined fault code is assigned a message to indicate the circuit, component, or system area that wasrcuit, component, or system area that wasdiagnosed as faulty. The messages are organized such that differdiagnosed as faulty. The messages are organized such that different messages related to a particularent messages related to a particularsensor or system are grouped together. Each group has a generic sensor or system are grouped together. Each group has a generic code as the first Code/Message thatcode as the first Code/Message thatindicates the generic nature of the fault. The manufacturer has indicates the generic nature of the fault. The manufacturer has a choice to define more specific DTC fora choice to define more specific DTC foreach lower level fault in that group. However only one Code musteach lower level fault in that group. However only one Code must be stored in OBD II for each faultbe stored in OBD II for each faultdetected. The manual gives examples of how to devise Codes to codetected. The manual gives examples of how to devise Codes to comply with the standard. mply with the standard. Appendix C of the manual gives theAppendix C of the manual gives the PowertrainPowertrain diagnostic trouble codes (diagnostic trouble codes (DTCsDTCs) as P codes. ) as P codes.

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Diagnostic Trouble Codes (SAE J 2012):

Data Link Security (SAE J 2186):SAE J 2186 defines the security practices that must be implementSAE J 2186 defines the security practices that must be implemented in accessing Diagnostic ed in accessing Diagnostic information only by authorized persons. The standard defines sevinformation only by authorized persons. The standard defines several levels of accessibility, like eral levels of accessibility, like secured functions, unsecured functions, and read only data. Thesecured functions, unsecured functions, and read only data. The emission related data is emission related data is accessible only to authorized personnel from EPA, responsible taccessible only to authorized personnel from EPA, responsible to ensure that the standard is o ensure that the standard is complied with.complied with.ComputerComputer--coded engine operating parameters shall not be changeable withoucoded engine operating parameters shall not be changeable without the use of t the use of specialized tools and procedures accessible to only authorized pspecialized tools and procedures accessible to only authorized persons.ersons.

Any reprogrammable computer code shall employ proven methods to Any reprogrammable computer code shall employ proven methods to deter unauthorized deter unauthorized reprogramming.reprogramming.

CARB and EPA require that enhanced tampering protection for the CARB and EPA require that enhanced tampering protection for the 1999 model year that shall 1999 model year that shall include data encryption and electronic access to manufacturer coinclude data encryption and electronic access to manufacturer computer for security access.mputer for security access.Procedure is defined to provide legislated “tamper protection”, Procedure is defined to provide legislated “tamper protection”, while meeting manufacturer while meeting manufacturer desired security concerns for tamper resistance and allowing legdesired security concerns for tamper resistance and allowing legitimate service.itimate service.One such technique enables certain operations such as Block downOne such technique enables certain operations such as Block download only if security access is load only if security access is successful. Normal communications are not affected.successful. Normal communications are not affected.

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Enhanced Test Modes (SAE J 2190):Enhanced Test Modes (SAE J 2190):SAE J 2190 extends the diagnostic test modes defined in SAE J 19SAE J 2190 extends the diagnostic test modes defined in SAE J 1979 to include access to emission79 to include access to emissionrelated data not included in SAE J 1979 and access to nonrelated data not included in SAE J 1979 and access to non--emission relate data as a supplement toemission relate data as a supplement toSAE J 1979. This standard describes the data byte values for diaSAE J 1979. This standard describes the data byte values for diagnostic messages transmitted between gnostic messages transmitted between diagnostic test equipment, either ondiagnostic test equipment, either on--vehicle or offvehicle or off--vehicle, and vehicle electronic modules. No distinction is made vehicle, and vehicle electronic modules. No distinction is made between emission and nonbetween emission and non--emission emission related diagnostics. These messages can be used with J 1850 datrelated diagnostics. These messages can be used with J 1850 data link as described in SAE J 1850 standard.a link as described in SAE J 1850 standard.SAE J 2190 includes test modes identified for diagnostics beyondSAE J 2190 includes test modes identified for diagnostics beyond minimum regulated requirements, that include nonminimum regulated requirements, that include non--emission systems. Test modes emission systems. Test modes include capabilities such as:include capabilities such as:

Request diagnostic sessionRequest diagnostic sessionRequest diagnostic “Freeze Frame” dataRequest diagnostic “Freeze Frame” dataRequest Diagnostic Trouble Codes/statusRequest Diagnostic Trouble Codes/statusClear diagnostic informationClear diagnostic informationRequest diagnostic dataRequest diagnostic dataSecurity accessSecurity accessDisable /enable normal message transmissionDisable /enable normal message transmissionRequest / define diagnostic data packetsRequest / define diagnostic data packetsEnter /exit diagnostic routineEnter /exit diagnostic routineRequest diagnostic routine resultsRequest diagnostic routine resultsInput /output controlInput /output controlRead /write block of memoryRead /write block of memory

Messages must be used with SAE J 1978 Scan Tool only using EDP pMessages must be used with SAE J 1978 Scan Tool only using EDP protocol, and with enhancedrotocol, and with enhanceddiagnostics tools.diagnostics tools.This activity is also coordinating with ISO diagnostic services This activity is also coordinating with ISO diagnostic services task force to promote common task force to promote common diagnostic capabilities throughout auto industry.diagnostic capabilities throughout auto industry.

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Enhanced E/E Diagnostic Test Modes: The following extended diagnostic Test modes are in force:The following extended diagnostic Test modes are in force:uuMode 10Mode 10-- Initiate diagnostic operation (limited)Initiate diagnostic operation (limited)uuMode 11Mode 11-- Request module resetRequest module resetuuMode 12Mode 12-- Request diagnostic “Freeze Frame “ dataRequest diagnostic “Freeze Frame “ datauuMode 13Mode 13-- Request DTC information Request DTC information uuMode 14 Mode 14 -- Clear diagnostic informationClear diagnostic informationuuMode 17Mode 17-- Request status ofRequest status of DTCsDTCsuuModeMode 1818-- RequestRequest DTCsDTCs by Statusby StatusuuMode 20 Mode 20 -- Return to Normal OperationReturn to Normal OperationuuMode 21Mode 21--23 23 -- Request Diagnostic Data by PID(s)Request Diagnostic Data by PID(s)uuMode 2A Mode 2A -- Request Diagnostic Data Packet(s)Request Diagnostic Data Packet(s)uuMode 2C Mode 2C -- Dynamically Define Diagnostic Data PacketDynamically Define Diagnostic Data PacketuuMode 3F Mode 3F -- Test Device PresentTest Device PresentuuMode 7F Mode 7F -- General response MessageGeneral response MessageuuMode AE Mode AE -- Request device ControlRequest device Control

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Enhanced E/E Diagnostic Test Modes:For each test mode this standard gives a functional description For each test mode this standard gives a functional description of the test, request message data byte content and report of the test, request message data byte content and report message data byte content , and an example for clarification message data byte content , and an example for clarification where necessary.where necessary.Physical addressing is used for all diagnostic messages in this Physical addressing is used for all diagnostic messages in this standard. Each device must be assigned a unique address in this standard. Each device must be assigned a unique address in this scheme which is the method J 1850 uses to communicate with scheme which is the method J 1850 uses to communicate with devices.devices.Messages 0 to FH and 40H to 4FH are reserved for SAE J 1979. Messages 0 to FH and 40H to 4FH are reserved for SAE J 1979. Messages for J 2190 start at 10H and end Messages for J 2190 start at 10H and end at FFH. The standard defines the message length, message at FFH. The standard defines the message length, message response requirement, and their formats. response requirement, and their formats.

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Universal Interface for OBD IIUniversal Interface for OBD II SCanSCan Tool:Tool:SAE J 2201 defines the vehicle communication interface for OBD ISAE J 2201 defines the vehicle communication interface for OBD II Scan Tool I Scan Tool described in SAE 1978. This interface connects the SAE J 1962 tedescribed in SAE 1978. This interface connects the SAE J 1962 test connector to the st connector to the hardware/software of the SAE 1978 OBD II Scan Tool which will uhardware/software of the SAE 1978 OBD II Scan Tool which will use this interface to se this interface to communicate with vehicles for accessing required OBD II functioncommunicate with vehicles for accessing required OBD II functions. The interface s. The interface defines several standard terms and interface functionality. The defines several standard terms and interface functionality. The standard describes in standard describes in detail the software requirements of the program in the PCM that detail the software requirements of the program in the PCM that facilitates facilitates communication between the Scan Tool (external) and the internal communication between the Scan Tool (external) and the internal OBD II OBD II components in the vehicle. The medium of communication is the secomponents in the vehicle. The medium of communication is the serial data link rial data link described in SAE J 1850. described in SAE J 1850. The standard defines the required message structure support, sigThe standard defines the required message structure support, signal ground, chassis nal ground, chassis ground, cable length of the Connector to Scan Tool, and other reground, cable length of the Connector to Scan Tool, and other requirements used by quirements used by SAE J 1978 Scan tool. SAE J 1978 Scan tool. Appendix A of the standard gives examples of interface implementAppendix A of the standard gives examples of interface implementation that have ation that have met the requirements of this standard.met the requirements of this standard.

Expanded Diagnostic Protocol for OBD II Scan Tools:Expanded Diagnostic Protocol for OBD II Scan Tools:

SAE J 2205 defines the expanded diagnostic protocol (EDP) for OBSAE J 2205 defines the expanded diagnostic protocol (EDP) for OBD II Scan Tool (SAE J 1978). The purpose of the expanded diagnosD II Scan Tool (SAE J 1978). The purpose of the expanded diagnostic protocol is to tic protocol is to define the encoding technique to be used:define the encoding technique to be used:

To describe to the OBD II Scan Tool the messages to be transmittTo describe to the OBD II Scan Tool the messages to be transmitted to a vehicle and how they are to be transmitted.ed to a vehicle and how they are to be transmitted.To describe to the OBD II Scan Tool the messages to be received To describe to the OBD II Scan Tool the messages to be received and processed by the Scan Tool.and processed by the Scan Tool.To describe to the OBD II Scan Tool how to process the data in To describe to the OBD II Scan Tool how to process the data in the received message. the received message.

This standard defines the requirements for diagnosis and serviceThis standard defines the requirements for diagnosis and service information to be provided by motor vehicle manufacturers. Appeinformation to be provided by motor vehicle manufacturers. Appendix A includes ndix A includes examples of the use of the EDP protocol that the Scan Tool mustexamples of the use of the EDP protocol that the Scan Tool must support.support. This includes at a minimum, supporting diagnosing and servicing This includes at a minimum, supporting diagnosing and servicing emissionemission--relatedrelatedcomponents and systems. EDP is a means for allowing vehicle mancomponents and systems. EDP is a means for allowing vehicle manufacturers to communicate, through the OBDufacturers to communicate, through the OBD II’sII’s communication interface, with communication interface, with vehicle modules using vehicle specific messages. vehicle modules using vehicle specific messages. The protocol will enable the service technician to input messageThe protocol will enable the service technician to input messages not required to meet specific OBD II requirements but which as not required to meet specific OBD II requirements but which are necessary to repair re necessary to repair vehicles. These additional messages will be specified in servicevehicles. These additional messages will be specified in service information provided to the service technician by the manufactuinformation provided to the service technician by the manufacturer. This is due to the rer. This is due to the requirement that vehicles must be able to be repaired using onlyrequirement that vehicles must be able to be repaired using only a SAE J 1978 Scan Tool and other nona SAE J 1978 Scan Tool and other non--microprocessor based tools.microprocessor based tools.The standard defines the functionality that will support the useThe standard defines the functionality that will support the use of the Scan Tool.of the Scan Tool.This standard provides the following EDP definitions:This standard provides the following EDP definitions:

Control typeControl typeTransmit typeTransmit typeReceive only typeReceive only typeMiscellaneous type Miscellaneous type

These message formats are defined in the standard. The codes forThese message formats are defined in the standard. The codes for EDP definition fields of the format are defined. Extensive messEDP definition fields of the format are defined. Extensive message format information age format information is included which needs to be supported by the Scan Tool. This sis included which needs to be supported by the Scan Tool. This standard requires that SAE J 1978 OBD II Scan Tool must support ttandard requires that SAE J 1978 OBD II Scan Tool must support the EDP messages he EDP messages which may be unique to a given vehicle manufacturer, model yearwhich may be unique to a given vehicle manufacturer, model year, etc. These messages may have different message headers, and di, etc. These messages may have different message headers, and different data fields fferent data fields compared to the SAE J 1979 message formats. The EDP must supportcompared to the SAE J 1979 message formats. The EDP must support ISO 9141ISO 9141--2 interface as well. The extended protocol regarding message f2 interface as well. The extended protocol regarding message formats, ormats, validation of data , data security, and other details are explaivalidation of data , data security, and other details are explained in the standard. ned in the standard.

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CLASS B Data Communications Network Interface CLASS B Data Communications Network Interface -- SAE J 1850:SAE J 1850:

CLASS B Data Communication Network Interface CLASS B Data Communication Network Interface -- SAE J 1850 standard defines the communication requirements of tSAE J 1850 standard defines the communication requirements of the he network that satisfies the needs of the vehicle manufacturers tonetwork that satisfies the needs of the vehicle manufacturers to perform OBD II functions in a cost effective manner.perform OBD II functions in a cost effective manner.

This standard describes two specific implementations of the netwThis standard describes two specific implementations of the network based on 10.4ork based on 10.4 KbpKbp/ Variable Pulse Width Type (VPW), / Variable Pulse Width Type (VPW), and another at 41.6and another at 41.6 KbpKbp/s Pulse Width Modification (PWM). The 10.4/s Pulse Width Modification (PWM). The 10.4 KbpKbp/s version uses single wire and the 41.6/s version uses single wire and the 41.6 KbpKbp/s uses /s uses 22--wire differential bus as the media/physical layer for message swire differential bus as the media/physical layer for message standard defines the physical layer and the data link layer of tandard defines the physical layer and the data link layer of the ISO (International standards Organization) open system Intthe ISO (International standards Organization) open system Interconnect (OSI) model. As a consequence this standard follows erconnect (OSI) model. As a consequence this standard follows the ISO conventions but uses different descriptive styles to dethe ISO conventions but uses different descriptive styles to define the message formats. The vehicle application for this classfine the message formats. The vehicle application for this class B B network is defined in SAE J 1213 to allow sharing of the vehiclenetwork is defined in SAE J 1213 to allow sharing of the vehicle parametric information. Also the class B network must be parametric information. Also the class B network must be capable of performing Class A network functions which operate capable of performing Class A network functions which operate at less than 10at less than 10 KbpKbp/s. /s.

J1850 data communication network interconnects different electroJ1850 data communication network interconnects different electronic modules on the vehicle using an Open architecture nic modules on the vehicle using an Open architecture approach. Open architecture approach allows addition or removalapproach. Open architecture approach allows addition or removal of any number of modules in the network without of any number of modules in the network without adverse effect on the network performance. J 1850 uses CSMA (caradverse effect on the network performance. J 1850 uses CSMA (carrier sense multiple access) protocol to implement Open rier sense multiple access) protocol to implement Open architecture. Additionally the network supports the architecture. Additionally the network supports the prioritization of message frames such that in case of contentioprioritization of message frames such that in case of contention, the higher priority frames win the arbitration and complete n, the higher priority frames win the arbitration and complete their transaction. The standard defines a singletheir transaction. The standard defines a single--bus topology where all the devices on the network transmit and rbus topology where all the devices on the network transmit and receive on a eceive on a single path at the same time with identical communication data. single path at the same time with identical communication data. The network uses aThe network uses a MasterlessMasterless bus control and priority bus control and priority arbitration. The consequence of this protocol is indeterminate larbitration. The consequence of this protocol is indeterminate latency and peak bus utilization profile, except the highest atency and peak bus utilization profile, except the highest priority message is guaranteed minimum latency at the expense ofpriority message is guaranteed minimum latency at the expense of other messages.other messages.

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CLASS B Data Communications Network Interface CLASS B Data Communications Network Interface -- SAE J 1850:SAE J 1850:

Although this standard focuses on the physical, and data link laAlthough this standard focuses on the physical, and data link layers in the OSI model, the yers in the OSI model, the application layer is also described since this needs to be incluapplication layer is also described since this needs to be included for emissionded for emission--related, related, diagnostic communication legislation requirements. The class B diagnostic communication legislation requirements. The class B network maps into the OSI network maps into the OSI model as illustrated in Figure 1 of the standard. The standard dmodel as illustrated in Figure 1 of the standard. The standard describes in detail the data link escribes in detail the data link layer’slayer’s diagnostic messages, their formats, physical addressing of the diagnostic messages, their formats, physical addressing of the devices, bus protocol devices, bus protocol commands, error detection and correction schemes. The physical dcommands, error detection and correction schemes. The physical dimensions of the network imensions of the network and its electrical characteristics are described in detail. and its electrical characteristics are described in detail.

Appendix A lists the applicationAppendix A lists the application--specific features. Appendix B defines the I/O EMC test plan specific features. Appendix B defines the I/O EMC test plan for the electro magnetic compatibility test to regulate electricfor the electro magnetic compatibility test to regulate electrical noise of the data signals. al noise of the data signals. Appendix C gives the VPW wave form analysis that specifies the dAppendix C gives the VPW wave form analysis that specifies the data signal wave form ata signal wave form characteristics for the 10.4characteristics for the 10.4 KbpKbp/s version. Appendix D gives the PWM wave form analysis that /s version. Appendix D gives the PWM wave form analysis that specifies the data signal wave form characteristics for the 41.6specifies the data signal wave form characteristics for the 41.6 KbpKbp/s version./s version.SAE J 1850 is the most important standard in the Data CommunicatSAE J 1850 is the most important standard in the Data Communication phase of the OBD II.ion phase of the OBD II.

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Class B Data Communication Network MessagesClass B Data Communication Network Messages-- Detailed Header Formats and Physical Detailed Header Formats and Physical Address Segments: (SAE J 2178/1): Address Segments: (SAE J 2178/1):

SAE J 2178/1, is the Class B Data Communication Network MessageSAE J 2178/1, is the Class B Data Communication Network Messages’ Detailed Header formats s’ Detailed Header formats and Physical Address Assignments specification. The standard defand Physical Address Assignments specification. The standard defines the information ines the information contained in the header and data fields of noncontained in the header and data fields of non--diagnostic messages. The standard also specifies diagnostic messages. The standard also specifies field sizes, scaling, representations, and data positions used field sizes, scaling, representations, and data positions used within messages. The general within messages. The general structure of the message frame is described withstructure of the message frame is described with inframeinframe response included in Figure 1 and response included in Figure 1 and without the response in Figure 2 of the standard. without the response in Figure 2 of the standard. SAE J 1979SAE J 1979 standard defines the information standard defines the information contained in the header and data fields of contained in the header and data fields of emission related diagnostic messagesemission related diagnostic messages. . SAE J 2190SAE J 2190standard defines the information contained in the header and datstandard defines the information contained in the header and data fields of a fields of other diagnostic other diagnostic messagesmessages not related to emissions. SAE J 1850 standard defines the classnot related to emissions. SAE J 1850 standard defines the class B network interface B network interface hardware, basic protocol definition, the electrical specificatiohardware, basic protocol definition, the electrical specifications, and the error detectionns, and the error detection--correction scheme using CRC (cyclic redundancy check) Byte. SAE correction scheme using CRC (cyclic redundancy check) Byte. SAE J 1850 defines only two J 1850 defines only two message formats. They are the single Byte format and the consolimessage formats. They are the single Byte format and the consolidated header format. The dated header format. The consolidated header format has two forms: a single Byte form, anconsolidated header format has two forms: a single Byte form, and a three byte form. This d a three byte form. This standard covers all these formats and forms to identify the constandard covers all these formats and forms to identify the contents of messages which can be tents of messages which can be sent on the SAE J 1850 network.sent on the SAE J 1850 network.

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Class B Data Communication Network MessagesClass B Data Communication Network Messages-- Detailed Header Formats and Physical Detailed Header Formats and Physical Address Segments: (SAE J 2178/1) (Address Segments: (SAE J 2178/1) (contdcontd):):

SAE J 2178 consists of four parts. SAE J 2178/1, the first part SAE J 2178 consists of four parts. SAE J 2178/1, the first part (this standard) describes the two allowed forms (this standard) describes the two allowed forms of message header formats, Single Byte, and Consolidated header of message header formats, Single Byte, and Consolidated header formats. This also contains the physical formats. This also contains the physical node address range assignments for the typical subsystems of thnode address range assignments for the typical subsystems of the automobile.e automobile.The standard defines the terms and definitions of the data formaThe standard defines the terms and definitions of the data formats. The overview of the standard is given in ts. The overview of the standard is given in Figure 3 of the standard. The system architecture for the differFigure 3 of the standard. The system architecture for the different possible headers used in class B are ent possible headers used in class B are described in sections 5 and 6. Section 7 defines the data fieldsdescribed in sections 5 and 6. Section 7 defines the data fields used by the different headerused by the different headerformats. section 8 defines the physical address assignments. Mesformats. section 8 defines the physical address assignments. Messages defined by this standard are classified sages defined by this standard are classified into two categories: Requests (commands: load or modify) or querinto two categories: Requests (commands: load or modify) or queries for data, and Responses, like reports or ies for data, and Responses, like reports or acknowledgments. The overall structure of messages is described acknowledgments. The overall structure of messages is described as follows:as follows:

Fully define SAE standard messagesFully define SAE standard messagesReserve messages for future SAE standardizationReserve messages for future SAE standardizationReserve messages for Manufacturers for their Unique messagesReserve messages for Manufacturers for their Unique messages

The message formats in this standard are mandatory for using J 1The message formats in this standard are mandatory for using J 1850 network except the many message 850 network except the many message codes reserved for manufacturers which are allocated can be usedcodes reserved for manufacturers which are allocated can be used..Appendix A describes two allowed network architectures, namely sAppendix A describes two allowed network architectures, namely single network, and multiple network ingle network, and multiple network architectures. architectures.

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Class B Data Communication Network MessagesClass B Data Communication Network Messages-- Data ParameterData Parameter DefintionsDefintions: (SAE J : (SAE J 2178/2):2178/2):

SAE J 2178/2 Data Parameter Definitions standard defines the parSAE J 2178/2 Data Parameter Definitions standard defines the parameters used to ameters used to describe the data variables used in normal vehicle operation as describe the data variables used in normal vehicle operation as well as diagnostic well as diagnostic operation. Parameters are assigned Parameter Reference Numbers (operation. Parameters are assigned Parameter Reference Numbers (PRNsPRNs) which are ) which are described in the standard. PRN structure is shown in Figure 3 indescribed in the standard. PRN structure is shown in Figure 3 in the standard. The the standard. The second part of the parameter definition is the SLOT. PRN identifsecond part of the parameter definition is the SLOT. PRN identifies a specific ies a specific parameter by name, unit measure , and its associated SLOT. The Sparameter by name, unit measure , and its associated SLOT. The SLOT defines the LOT defines the mathematical characteristic of parameters in terms of its numermathematical characteristic of parameters in terms of its numeric presentation, its ic presentation, its scaling, its limits, Offsets, and its transfer function.scaling, its limits, Offsets, and its transfer function.Appendix A and B provide cross references to find the PRN by theAppendix A and B provide cross references to find the PRN by the number or by number or by name. PRN structure is given in Figure 3. SAE J 1979 refers to Pname. PRN structure is given in Figure 3. SAE J 1979 refers to PID numbers which ID numbers which are single byte reference number. The first 256are single byte reference number. The first 256 PRNsPRNs defined in this standard are defined in this standard are identical to the SAE J 1979 PID definitions. The standard contaiidentical to the SAE J 1979 PID definitions. The standard contains detailed lists of ns detailed lists of PRN assignments which are used for reference.PRN assignments which are used for reference.

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Class B Data Communication Network MessagesClass B Data Communication Network Messages-- Frame IDs For Single Byte Forms Frame IDs For Single Byte Forms of Headers (SAE J 2178/3):of Headers (SAE J 2178/3):

SAE J 2178/3 Frame IDs for Single Byte Forms of Headers standarSAE J 2178/3 Frame IDs for Single Byte Forms of Headers standard, defines the messages specified for d, defines the messages specified for networks using one byte header or the single byte form of the conetworks using one byte header or the single byte form of the consolidated header as specified in SAE J 1850. nsolidated header as specified in SAE J 1850. This standard focuses on the Frame ID which is the first byte ofThis standard focuses on the Frame ID which is the first byte of the message. The first byte of the one byte the message. The first byte of the one byte header is defined as an 8 bit hexadecimal number, and the first header is defined as an 8 bit hexadecimal number, and the first byte of the single byte form of the byte of the single byte form of the consolidated header is defined under 7 bits as hexadecimal numbeconsolidated header is defined under 7 bits as hexadecimal number. The information in the header field r. The information in the header field implicitly defines the target, source, priority, and message typimplicitly defines the target, source, priority, and message type information, while the data field contains e information, while the data field contains additional addressing and parametric information. The header defadditional addressing and parametric information. The header defines the Message identifier or Frame ID ines the Message identifier or Frame ID and becomes the name that is broadcast normally periodically to and becomes the name that is broadcast normally periodically to all the nodes on the network. all the nodes on the network.

This standard describes the overall structure of messages and haThis standard describes the overall structure of messages and has wide application in OBD II since these have s wide application in OBD II since these have to be used on J 1850 exactly as they are specified here, except to be used on J 1850 exactly as they are specified here, except those that are allocated to vehicle manufacturers those that are allocated to vehicle manufacturers for nonfor non--emission related messages.emission related messages.

With single byte form of header, the Frame ID corresponds to theWith single byte form of header, the Frame ID corresponds to the PRN number or a grouping ofPRN number or a grouping of PRNsPRNs. The . The characteristics defined by the header are described in the standcharacteristics defined by the header are described in the standard. Figure 3 of the standard defines the ard. Figure 3 of the standard defines the Frame ID for one byte headers and the first byte of the single bFrame ID for one byte headers and the first byte of the single byte form of the consolidated header.yte form of the consolidated header.

Class B Data Communication Network MessagesClass B Data Communication Network Messages-- Message Definition for Three Byte Message Definition for Three Byte Headers (SAE J 2178/4):Headers (SAE J 2178/4):

SAE J 2178/4 Message Definition for Three Byte Headers, standardSAE J 2178/4 Message Definition for Three Byte Headers, standard defines the information defines the information contained in the header and the data fields of noncontained in the header and the data fields of non--diagnostic messages for SAE J 1850 data diagnostic messages for SAE J 1850 data communication class B networks. This standard describes and speccommunication class B networks. This standard describes and specifies the header fields, data ifies the header fields, data fields, field sizes, scaling, representations, and data positionfields, field sizes, scaling, representations, and data positions used within messages. SAE J 1979 s used within messages. SAE J 1979 standard defines the specifications of emissionstandard defines the specifications of emission--related diagnostic message header and data related diagnostic message header and data fields which OBD II is mainly concurred with. SAE J 2190 definesfields which OBD II is mainly concurred with. SAE J 2190 defines other diagnostic data fields. other diagnostic data fields. This standard focuses on the message definition for the three byThis standard focuses on the message definition for the three byte form of the consulted header te form of the consulted header format. Section 5 of this standard provides the list of functionformat. Section 5 of this standard provides the list of functional target addresses or Primary IDs al target addresses or Primary IDs for all of the functionally addressed messages on J 1850 exceptfor all of the functionally addressed messages on J 1850 except type #3, which is Function Read. type #3, which is Function Read. SAE J 1850 type # 3 messages have a separate address assignment SAE J 1850 type # 3 messages have a separate address assignment due to absence of secondary due to absence of secondary addressing. Section 6 of the standard shows the valid extended aaddressing. Section 6 of the standard shows the valid extended address assignments from the ddress assignments from the message definition tables. Section 7 lists the secondary messagemessage definition tables. Section 7 lists the secondary message definitions. The information in definitions. The information in this standard follows the same format as the Frame IDs for Singlthis standard follows the same format as the Frame IDs for Single Byte Forms of Headerse Byte Forms of Headersin SAE J 2178/3 standard described above.

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in SAE J 2178/3 standard described above.

Fundamentals ofFundamentals of PowertrainPowertrainControl strategies & OBD II Control strategies & OBD II DiagnosticsDiagnostics

Since OBD II became effective in 1994 ( adopted from CARB regulaSince OBD II became effective in 1994 ( adopted from CARB regulations),tions),powertrainpowertrain control strategies are focused on monitoringcontrol strategies are focused on monitoring powertrainpowertraincomponents for failures with criteria tied to emission levels incomponents for failures with criteria tied to emission levels in addition to addition to basic functionality. All thebasic functionality. All the powertrainpowertrain components described in previous components described in previous section onsection on PowertrainPowertrain and Emission Controls in Passenger vehicles and Emission Controls in Passenger vehicles including sensors, actuators, and switches are checked for corrincluding sensors, actuators, and switches are checked for correct operation. ect operation. In addition the performance of emission control apparatus are coIn addition the performance of emission control apparatus are continuously ntinuously monitored using OBD II Diagnostics criteria. The following is a monitored using OBD II Diagnostics criteria. The following is a list of the list of the major CARB related OBD I I diagnostic requirements for all vehicmajor CARB related OBD I I diagnostic requirements for all vehicle le manufacturers:manufacturers:

Fundamentals ofFundamentals of PowertrainPowertrainControl strategies & OBD II Control strategies & OBD II DiagnosticsDiagnostics

OBD I I Diagnostic RequirementsOBD I I Diagnostic RequirementsuuEngine Misfire DetectionEngine Misfire DetectionuuCatalyst Efficiency MonitorCatalyst Efficiency MonitoruuOxygen Sensor & Heater MonitoringOxygen Sensor & Heater MonitoringuuFuel System MonitoringFuel System MonitoringuuEvaporative System MonitoringEvaporative System MonitoringuuEGR System MonitoringEGR System MonitoringuuSecondary Air System MonitoringSecondary Air System MonitoringuuComprehensive Components Monitoring (all sensors, Comprehensive Components Monitoring (all sensors, actuators, and switches)actuators, and switches)

Engine Misfire Detection: Misfiring is the lack of combustion inEngine Misfire Detection: Misfiring is the lack of combustion in the cylinder. Misfiring can be caused by worn ignition the cylinder. Misfiring can be caused by worn ignition components, poor fuel metering, or faulty electrical system. Exccomponents, poor fuel metering, or faulty electrical system. Excessive exhaust emissions will be the result even with few essive exhaust emissions will be the result even with few misfires. Increased misfire rates can damage the catalytic convmisfires. Increased misfire rates can damage the catalytic converter. Engine misfire is detected by monitoring crankshaft speederter. Engine misfire is detected by monitoring crankshaft speedfluctuations. Engine misfire will fluctuations. Engine misfire will contribute to a deceleration of the crankshaft’s rotational speecontribute to a deceleration of the crankshaft’s rotational speed due to the momentary absence of engine torque during thed due to the momentary absence of engine torque during thepowerstrokepowerstroke of the cylinder that is misfiring. Using the crankshaft sensor of the cylinder that is misfiring. Using the crankshaft sensor input, theinput, theinstantaneous crankshaft speed is calculated, and the speed signinstantaneous crankshaft speed is calculated, and the speed signal is analyzed to detect the misfire. To eliminate other causes al is analyzed to detect the misfire. To eliminate other causes of of torque reduction due to rough roads and other driving events, thtorque reduction due to rough roads and other driving events, the speed reduction is monitored using Exponentially weighted e speed reduction is monitored using Exponentially weighted moving average (EWMA) technique to identify the misfiring cylindmoving average (EWMA) technique to identify the misfiring cylinder. Other techniques used to identify torque reduction due to er. Other techniques used to identify torque reduction due to misfire, include signal processing using several algorithms. Onemisfire, include signal processing using several algorithms. One signal processing method analyzes the amplitude and phase of signal processing method analyzes the amplitude and phase of each of the first twelve frequency components of the crankshaft each of the first twelve frequency components of the crankshaft angular velocity signal taken continuously during the torque angular velocity signal taken continuously during the torque reduction time. If a certain percent of misfires within 200 or 1reduction time. If a certain percent of misfires within 200 or 1000 revolutions is detected , a fault code (DTC) is set. Misfire000 revolutions is detected , a fault code (DTC) is set. Misfire is is detected if the offending cylinder can be identified. Other advdetected if the offending cylinder can be identified. Other advanced signal processing algorithms can be used such as Principalanced signal processing algorithms can be used such as PrincipalComponent Analysis and Clustering to compress the data and isolaComponent Analysis and Clustering to compress the data and isolate the misfiring cylinder.te the misfiring cylinder.If a misfire is detected, all the main engine operating parameteIf a misfire is detected, all the main engine operating parameters such as engine speed , engine load or MAP (Manifold absolute rs such as engine speed , engine load or MAP (Manifold absolute Pressure), engine coolant temperature, throttle position, oxygePressure), engine coolant temperature, throttle position, oxygen sensor, values are stored away in memory. This is called n sensor, values are stored away in memory. This is called “Freeze Frame”, which is an OBD II requirement. Freeze Frame is “Freeze Frame”, which is an OBD II requirement. Freeze Frame is used to identify a consecutive misfire in the next driving cycleused to identify a consecutive misfire in the next driving cycledefined by the EPA as the next driving “Trip” after ignition OFFdefined by the EPA as the next driving “Trip” after ignition OFF. If a second misfire is detected the engine controller will tur. If a second misfire is detected the engine controller will turn n on the MIL (Malfunction Indicator Light) to alert the driver. Thon the MIL (Malfunction Indicator Light) to alert the driver. The specific cylinder experiencing misfire must be identified. If e specific cylinder experiencing misfire must be identified. If more than one cylinder is misfiring a separate DTI (diagnostic tmore than one cylinder is misfiring a separate DTI (diagnostic trouble code) is required.rouble code) is required.If misfire is not detected during the next three subsequent coIf misfire is not detected during the next three subsequent consecutive driving “Trips” when similar conditions occur then thensecutive driving “Trips” when similar conditions occur then theoriginal fault will be erased and the MIL will be turned off by original fault will be erased and the MIL will be turned off by the engine controller. In another circumstance , if “similar the engine controller. In another circumstance , if “similar conditions” are not encountered during next eighty subsequent trconditions” are not encountered during next eighty subsequent trips the original fault will be turned off by the engine ips the original fault will be turned off by the engine controller. controller.

The Freeze Frame can also be used for OffThe Freeze Frame can also be used for Off--Board diagnostics and trouble shooting by service technicians.Board diagnostics and trouble shooting by service technicians.Misfires can damage the catalyst converters by raising the catalMisfires can damage the catalyst converters by raising the catalyst temperature beyond safe values.yst temperature beyond safe values.Type A misfire is defined below:Type A misfire is defined below:For type A misfire, up to three 200 revolutions are evaluated onFor type A misfire, up to three 200 revolutions are evaluated on first driving cycle for misfire detectionfirst driving cycle for misfire detectionbefore illuminating MIL. before illuminating MIL. MIL must be illuminated on misfire detection during first 200 reMIL must be illuminated on misfire detection during first 200 revolutions’ evaluation during the second driving cycle.volutions’ evaluation during the second driving cycle.However MIL need not be steadily illuminated when misfire ceasesHowever MIL need not be steadily illuminated when misfire ceases, until second driving cycle., until second driving cycle.Type B misfire (during starting of engine):Type B misfire (during starting of engine):This misfire is evaluated in first 1000 revolutions after engineThis misfire is evaluated in first 1000 revolutions after engine is started. Misfire detection will set coolant temperature is started. Misfire detection will set coolant temperature fault code since that is the likely cause of misfire detection afault code since that is the likely cause of misfire detection at this time.t this time.MIL and “hard” fault code is set permanently on second driving cMIL and “hard” fault code is set permanently on second driving cycle.ycle.Up to four 1000 revolutions are evaluated for misfire detection Up to four 1000 revolutions are evaluated for misfire detection excluding the first 1000 revolutionsexcluding the first 1000 revolutionsbefore illuminating temperature fault code. before illuminating temperature fault code. MIL and “hard code” are set on second driving cycle. MIL and “hard code” are set on second driving cycle. Thermostat (coolant temperature) monitoring and misfire detectioThermostat (coolant temperature) monitoring and misfire detection monitoring are extremely important due to n monitoring are extremely important due to increasingly tighter controls mandated on emissions.increasingly tighter controls mandated on emissions.Misfire detection is described in more detail in a later sectionMisfire detection is described in more detail in a later section..

Catalyst Efficiency Monitor: There are three types of catalysts:Catalyst Efficiency Monitor: There are three types of catalysts: pellet (bead), ceramic monolith, and metal monolith. They diffepellet (bead), ceramic monolith, and metal monolith. They differ r in the method by which they support the noble metals which convein the method by which they support the noble metals which convert exhaust gases to HC andrt exhaust gases to HC and NOxNOx free gases. Threefree gases. Three--way way catalytic converters typically contain platinum, and/or palladicatalytic converters typically contain platinum, and/or palladium, along with rhodium as catalytic materials. The term threeum, along with rhodium as catalytic materials. The term three--way refers to the ability of the converter to simultaneously oxiway refers to the ability of the converter to simultaneously oxidize HC and CO and reducedize HC and CO and reduce NOxNOx. Catalyst converters operate . Catalyst converters operate efficiently within a prescribed temperature range when placed atefficiently within a prescribed temperature range when placed at proper location in the exhaust gases’ path. Operation at proper location in the exhaust gases’ path. Operation at temperatures which exceed the recommended maximums may cause irrtemperatures which exceed the recommended maximums may cause irreversible damage to the catalyst, and components of the eversible damage to the catalyst, and components of the converter. Since unburned fuel into the converter can cause catconverter. Since unburned fuel into the converter can cause catastrophic failure, misfire detection is a must for safe converteastrophic failure, misfire detection is a must for safe converter r operation. Misfire detection is described previously. Converter operation. Misfire detection is described previously. Converter also must have an over temperature detection algorithm to also must have an over temperature detection algorithm to detect excessive temperature in the converter. This is done by ddetect excessive temperature in the converter. This is done by decreasing the A/F ratio’s lambda value to less than 1. This ecreasing the A/F ratio’s lambda value to less than 1. This algorithm cannot work foralgorithm cannot work for coastdowncoastdown conditions or overrun conditions. Therefore Deceleration fuel cconditions or overrun conditions. Therefore Deceleration fuel cutoff (DFCO) is sued to utoff (DFCO) is sued to control catalyst temperature during vehiclecontrol catalyst temperature during vehicle coastdowncoastdown, when the engine intake manifold pressure is drive too low to a, when the engine intake manifold pressure is drive too low to allow llow complete combustion. To prevent unburned fuel from entering the complete combustion. To prevent unburned fuel from entering the converter, the fuel injectors are shut off by the engine converter, the fuel injectors are shut off by the engine controller. Spark advance is filtered and thresholds are set to controller. Spark advance is filtered and thresholds are set to control torque reversal ”bump” while still protecting the convercontrol torque reversal ”bump” while still protecting the converter. ter. The catalyst monitor evaluates the converter efficiency as mandaThe catalyst monitor evaluates the converter efficiency as mandated by the OBD II to ensure that the catalyst is cleaning up theted by the OBD II to ensure that the catalyst is cleaning up theexhaust gases and reducing emissions from the exhaust gases. Theexhaust gases and reducing emissions from the exhaust gases. The diagnostic evaluates the oxygen storage capacity of the diagnostic evaluates the oxygen storage capacity of the converter by comparing the signal output of the postconverter by comparing the signal output of the post--converter oxygen sensor with the preconverter oxygen sensor with the pre--converter oxygen sensor. According converter oxygen sensor. According to EPA regulations, a catalyst is regarded as malfunctioning wheto EPA regulations, a catalyst is regarded as malfunctioning when the average hydrocarbon conversion efficiency falls between n the average hydrocarbon conversion efficiency falls between 50 and 60%. The diagnostic system is required to detect when the50 and 60%. The diagnostic system is required to detect when the hydrocarbon emission (HC) concentration of the catalyst hydrocarbon emission (HC) concentration of the catalyst (closest to the engine ) is more than 40 to 50% of the engine(closest to the engine ) is more than 40 to 50% of the engine--out emission concentration. The check is performed with the vehiout emission concentration. The check is performed with the vehicle cle operating at between 20 and 50 miles/hr with the speed held at operating at between 20 and 50 miles/hr with the speed held at a reasonably steady state condition. The output signal wave a reasonably steady state condition. The output signal wave form of the oxygen sensor (lambda sensor) ,at the front end of tform of the oxygen sensor (lambda sensor) ,at the front end of the converter close to the engine,he converter close to the engine, oscillates between lean and rich oscillates between lean and rich value of 100value of 100 millivoltsmillivolts and 900and 900 millivoltsmillivolts due to closeddue to closed--loop control strategy that keeps the Air/Fuel ratio atloop control strategy that keeps the Air/Fuel ratio at stoichiometrystoichiometry(lambda value equal to 1). For a converter whose oxygen storag(lambda value equal to 1). For a converter whose oxygen storage capacity is good, the output of the oxygen signal at the far ee capacity is good, the output of the oxygen signal at the far end nd of the converter should be flat, without any oscillation. This iof the converter should be flat, without any oscillation. This is due to the converter’s ability to store oxygen when the gas iss due to the converter’s ability to store oxygen when the gas is lean lean (and rich in oxygen) and give up oxygen when the gas is rich (an(and rich in oxygen) and give up oxygen when the gas is rich (and short of oxygen). This characteristic enables the oxidation ofd short of oxygen). This characteristic enables the oxidation ofhydrocarbons and the reduction ofhydrocarbons and the reduction of NOxNOx in the exhaust gas simultaneously. The diagnostic consists of min the exhaust gas simultaneously. The diagnostic consists of measuring the average easuring the average ripple in the output signal wave form of the oxygen sensor at thripple in the output signal wave form of the oxygen sensor at the far end of the converter and comparing the ripple with a e far end of the converter and comparing the ripple with a similar oscillation at the input signal wave form of the oxygen similar oscillation at the input signal wave form of the oxygen sensor at the near end (closest to the engine) of the converter.sensor at the near end (closest to the engine) of the converter. If If the difference is above a value that corresponds to more than 6the difference is above a value that corresponds to more than 60% converter efficiency then the converter efficiency is 0% converter efficiency then the converter efficiency is considered good. As a second check the catalyst temperature at tconsidered good. As a second check the catalyst temperature at the outlet is monitored and compared to the catalyst he outlet is monitored and compared to the catalyst temperature at the input to the converter. If the catalyst is futemperature at the input to the converter. If the catalyst is functioning properly, it creates an exothermic reaction resulting nctioning properly, it creates an exothermic reaction resulting in a in a higher outlet catalyst temperature. But this is not always reliahigher outlet catalyst temperature. But this is not always reliable. The sensitivity of the outlet gas temperature to catalyst ble. The sensitivity of the outlet gas temperature to catalyst efficiency may be too low to reliably detect the difference at tefficiency may be too low to reliably detect the difference at the 60% HC conversion efficiency level. he 60% HC conversion efficiency level. Signal characteristics from the oxygen sensors for fresh, degradSignal characteristics from the oxygen sensors for fresh, degraded, and failed catalysts are explained in detail in a later seced, and failed catalysts are explained in detail in a later section.tion.The misfire detection diagnostic which is previously described iThe misfire detection diagnostic which is previously described is an important preventive measure that protects the converter s an important preventive measure that protects the converter from extreme temperature spike that can severely reduce convertefrom extreme temperature spike that can severely reduce converter efficiency or even cause catalyst destruction altogether.r efficiency or even cause catalyst destruction altogether.Catalyst converter diagnostics are described in more detail in aCatalyst converter diagnostics are described in more detail in a later section.later section.

Fundamentals ofFundamentals of PowertrainPowertrainControl strategies & OBD II Control strategies & OBD II DiagnosticsDiagnostics

Oxygen Sensor & Heater Monitoring: An oxygen sensor performs besOxygen Sensor & Heater Monitoring: An oxygen sensor performs best when its operating temperature is maintained within a specifict when its operating temperature is maintained within a specific range above 260range above 260OO C. For this reason a C. For this reason a heater is used to keep the oxygen sensor temperature at the desiheater is used to keep the oxygen sensor temperature at the desired value. red value. The OBD II diagnostic requires that the heater of the oxygen senThe OBD II diagnostic requires that the heater of the oxygen sensor must be monitored periodically for its normal operation. Thesor must be monitored periodically for its normal operation. The circuit continuity is checked, the voltage circuit continuity is checked, the voltage across the heater is checked, the current carried by the heater across the heater is checked, the current carried by the heater element is checked ( Max. 20 A), as well as the temperature of telement is checked ( Max. 20 A), as well as the temperature of the oxygen sensor. For added reliability, the he oxygen sensor. For added reliability, the heater is directly controlled by the the controller without anyheater is directly controlled by the the controller without any relay. If the heater is found defective on any of these accountrelay. If the heater is found defective on any of these accounts, the PCM sets a fault code.s, the PCM sets a fault code.The PCM has a special input circuit for detecting short circuit The PCM has a special input circuit for detecting short circuit or open circuit (break) of the sensor wiring and monitors the swor open circuit (break) of the sensor wiring and monitors the switching frequency (closeditching frequency (closed--loop) of the control loop) of the control loop.loop.Oxygen sensor diagnostic requires the following checks: Circuit Oxygen sensor diagnostic requires the following checks: Circuit continuity ,and the bias voltage of 450continuity ,and the bias voltage of 450 millivoltsmillivolts in the sensor circuit are verified. The voltage across the in the sensor circuit are verified. The voltage across the sensor should read 450sensor should read 450 millivoltsmillivolts with the ignition key On and engine not started. If the voltagewith the ignition key On and engine not started. If the voltage is not present a fault code (DTC) isis not present a fault code (DTC) isset. During the closed loop operation of the vehicle, after theset. During the closed loop operation of the vehicle, after the sensor attains the operating temperature (above 300sensor attains the operating temperature (above 300OO C ), the sensor voltage should oscillate between about C ), the sensor voltage should oscillate between about

100 to 250100 to 250 mvmv at the low end and 700 to 900at the low end and 700 to 900 mvmv at the high end. The frequency of oscillation of this sensor voat the high end. The frequency of oscillation of this sensor voltage is between 1.25 Hz to 2.5 Hz, depending upon the fuel ltage is between 1.25 Hz to 2.5 Hz, depending upon the fuel controller, fuel injection system, and vehicle operation. If thecontroller, fuel injection system, and vehicle operation. If the oscillation is slower than normal meaning that the oxygen sensooscillation is slower than normal meaning that the oxygen sensor is responding slowly to the A/F ratio input, r is responding slowly to the A/F ratio input, then it is due to the sensor being exposed to high heat for a lothen it is due to the sensor being exposed to high heat for a long period of time. This can cause a deviation in the A/F ratio fng period of time. This can cause a deviation in the A/F ratio from the optimumrom the optimum stoichiometrystoichiometry value, value, resulting in increased emissions. The deviation can be detectedresulting in increased emissions. The deviation can be detected by monitoring the signal output oscillation of upstream oxygen by monitoring the signal output oscillation of upstream oxygen (lambda) sensor and comparing it with the (lambda) sensor and comparing it with the system operation frequency (1.25 Hz to 2.5 Hz) obtained from thsystem operation frequency (1.25 Hz to 2.5 Hz) obtained from the controller. A fault code is stored if the oxygen sensor at thee controller. A fault code is stored if the oxygen sensor at the upstream of the converter is oscillating upstream of the converter is oscillating slower than the system frequency. A MIL is also illuminated. Addslower than the system frequency. A MIL is also illuminated. Additionally the controller compares the output signal (voltage) ofitionally the controller compares the output signal (voltage) of the additional lambda sensor downstream the additional lambda sensor downstream of the converter with the oxygen (lambda) sensor signal upstreamof the converter with the oxygen (lambda) sensor signal upstream. Using this information the controller can detect deviations of. Using this information the controller can detect deviations of the average value in the A/F ratio that the average value in the A/F ratio that determines the system frequency. If system is operating rich anddetermines the system frequency. If system is operating rich and the lambda sensor indicates lean, then it is misfire problem. Ithe lambda sensor indicates lean, then it is misfire problem. If system is operating lean, and the lambda f system is operating lean, and the lambda sensor voltage stays near bias (450sensor voltage stays near bias (450 mvmv) and engine does not go into closed loop, the sensor is having ) and engine does not go into closed loop, the sensor is having an open circuit and is defective. Slow transient response in A/Fan open circuit and is defective. Slow transient response in A/F shift shift can also be caused by fuel control problem or carbon deposits orcan also be caused by fuel control problem or carbon deposits or due to mild driving mode. Fuel system must be checked before dedue to mild driving mode. Fuel system must be checked before deciding that oxygen sensor is faulty. If the ciding that oxygen sensor is faulty. If the A/F ratio is fluctuating due to excessive correction, to the preA/F ratio is fluctuating due to excessive correction, to the pre set data map of optimum fuel required for each load and engine set data map of optimum fuel required for each load and engine RPM, provided by the oxygen sensor, it is an RPM, provided by the oxygen sensor, it is an indication of a faulty fuel system. The OBD II legal requirementindication of a faulty fuel system. The OBD II legal requirements are: The diagnostic system shall monitor the output voltage, ts are: The diagnostic system shall monitor the output voltage, the response rate, and any other parameter he response rate, and any other parameter that can affect emissions, and all fuel control oxygen sensors fthat can affect emissions, and all fuel control oxygen sensors for malfunction.or malfunction.all fuel control oxygen sensors for malfunction. In case of a faall fuel control oxygen sensors for malfunction. In case of a faulty sensor the MIL shall be illuminated and the DTC shall be stulty sensor the MIL shall be illuminated and the DTC shall be stored in the computer.ored in the computer.Oxygen sensor diagnostics are described in more detail in a lateOxygen sensor diagnostics are described in more detail in a later section.r section.

Fundamentals ofFundamentals of PowertrainPowertrainControl strategies & OBD II Control strategies & OBD II DiagnosticsDiagnostics

Fuel System MonitoringFuel System Monitoring: For fuel control strategies multipoint pulsed fuel injection s: For fuel control strategies multipoint pulsed fuel injection system is assumed. Theystem is assumed. The powertrainpowertrain control strategy is to provide the control strategy is to provide the correct Air/Fuel ratio under all operating conditions, except ducorrect Air/Fuel ratio under all operating conditions, except during coldring cold--start. The systems involved in this control are fuel metering, fstart. The systems involved in this control are fuel metering, fuel pump, ignition uel pump, ignition timing, fuel injectors, injector pulse width, and lambda controltiming, fuel injectors, injector pulse width, and lambda control. The PCM determines the required injector pulse width to maint. The PCM determines the required injector pulse width to maintain Air/Fuel ratio within ain Air/Fuel ratio within the lambda control window (0.93 to 1.07). The PCM adds correctiothe lambda control window (0.93 to 1.07). The PCM adds correction factors ton factors to injectiorinjectior pulse width to increase fuel injection during cold start, and wpulse width to increase fuel injection during cold start, and wide ide open throttle, in closedopen throttle, in closed--loop operation. During deceleration, PCM closes fuel injection. loop operation. During deceleration, PCM closes fuel injection. Ignition timing affects emissions. Excessive spark advance will Ignition timing affects emissions. Excessive spark advance will cause engine knock. consequently fuel system monitoring is donecause engine knock. consequently fuel system monitoring is done by using predetermined data map with optimal fuel required for by using predetermined data map with optimal fuel required for each load (MAP each load (MAP value) and engine RPM point. The amount of fuel is determined byvalue) and engine RPM point. The amount of fuel is determined by the duty cycle of the injector pulse width. the duty cycle of the injector pulse width.

The lambda closedThe lambda closed--loop control system provides feedback to the PCM on the necessarloop control system provides feedback to the PCM on the necessary correction to the preset data points. The corrected informatioy correction to the preset data points. The corrected information n is stored in theis stored in the PCM’sPCM’s memory so that the next time that operation point is reached, lmemory so that the next time that operation point is reached, less correction of the Air/Fuel ratio will be required. If the PCess correction of the Air/Fuel ratio will be required. If the PCM M correction passes a predetermined threshold, it indicates a faulcorrection passes a predetermined threshold, it indicates a faulty fuel system, that some component in the fuel supply system isty fuel system, that some component in the fuel supply system is outside of its operating outside of its operating range. Some possibilities are defective fuel pressure regulator,range. Some possibilities are defective fuel pressure regulator, contaminated fuel injectors, defective manifold absolute pressucontaminated fuel injectors, defective manifold absolute pressure (MAP) sensor, intake air re (MAP) sensor, intake air system leakage, or exhaust system leakage. All electronic composystem leakage, or exhaust system leakage. All electronic components are checked for circuit continuity, rated current, rated vnents are checked for circuit continuity, rated current, rated voltage, and rational oltage, and rational parameter values within limits of operation. These include fuel parameter values within limits of operation. These include fuel pump, ignition circuit, injection solenoids, engine RPM sensor, pump, ignition circuit, injection solenoids, engine RPM sensor, and MAP sensor. If the and MAP sensor. If the fuel correction exceeds the limit, either in absolute value or ifuel correction exceeds the limit, either in absolute value or in update rate, the fuel system is deemed faulty and a fault coden update rate, the fuel system is deemed faulty and a fault code is stored and MIL is is stored and MIL is illuminated. Since fuel system has a major impact on emissions, illuminated. Since fuel system has a major impact on emissions, its diagnostics are crucial to control emissions and consequentlits diagnostics are crucial to control emissions and consequently to OBD II.y to OBD II.The legal OBD II requirements are: The diagnostic system shall mThe legal OBD II requirements are: The diagnostic system shall monitor the fuel delivery system for its ability to provide complonitor the fuel delivery system for its ability to provide compliance with emission iance with emission standards.standards.

Diagnostic technique: Deviations of theDiagnostic technique: Deviations of the stoichiometricstoichiometric ratio which last for a longer time are stored within the adaptiratio which last for a longer time are stored within the adaptive mixture controller. If these ve mixture controller. If these values exceed defined limits, components of the fuel system are values exceed defined limits, components of the fuel system are deemed faulty. MIL is illuminated at that time. Fuel system diadeemed faulty. MIL is illuminated at that time. Fuel system diagnostics are described in gnostics are described in more detail in a later section.more detail in a later section.

Evaporative System Monitoring:Evaporative System Monitoring: Hydro Carbons (HC) in the form of fuel vapors escaping from thHydro Carbons (HC) in the form of fuel vapors escaping from the vehicle, primarily from the e vehicle, primarily from the fuel tank are required to be monitored to reduce emissions as lefuel tank are required to be monitored to reduce emissions as legislated by EPA and required by OBD II. There are two principal gislated by EPA and required by OBD II. There are two principal causes of fuel vapor in the fuel tank: increasing ambient tempercauses of fuel vapor in the fuel tank: increasing ambient temperature and return of unused hot fuel from the engine. The ature and return of unused hot fuel from the engine. The evaporative control system consists of a vapor ventilation line evaporative control system consists of a vapor ventilation line that exits the fuel tank and enters fuel vapor canister. The canthat exits the fuel tank and enters fuel vapor canister. The canister ister consists of an active charcoal element which absorbs the vapor aconsists of an active charcoal element which absorbs the vapor and allows only air to escape to the atmosphere. Only a certain nd allows only air to escape to the atmosphere. Only a certain volume of fuel vapor can be contained by the canister. The vaporvolume of fuel vapor can be contained by the canister. The vapors in the canister must therefore be purged into the engine and s in the canister must therefore be purged into the engine and burned by the engine so that the canister can continue to store burned by the engine so that the canister can continue to store vapors when they are generated.vapors when they are generated.To accomplish this another purge line leads from the char coal cTo accomplish this another purge line leads from the char coal canister to the intake manifold. Included in this line is the anister to the intake manifold. Included in this line is the canister purge solenoid valve. The layout of a typical evaporaticanister purge solenoid valve. The layout of a typical evaporative emission control system is described in a later section.ve emission control system is described in a later section.During engine operation vacuum in the intake manifold causes floDuring engine operation vacuum in the intake manifold causes flow through the charcoal canister because the canister vent w through the charcoal canister because the canister vent opening at the charcoal filter end is at atmospheric pressure. Topening at the charcoal filter end is at atmospheric pressure. The canister purge valve meters the amount of flow from the he canister purge valve meters the amount of flow from the canister. The amount of fuel vapor in the canister and thereforecanister. The amount of fuel vapor in the canister and therefore, contained in the flow stream, is not known. Therefore it is , contained in the flow stream, is not known. Therefore it is critical that the lambda control system is operating and adjusticritical that the lambda control system is operating and adjusting the fuel requirement as the vapors are being purged. Purge ng the fuel requirement as the vapors are being purged. Purge vapors could otherwise result invapors could otherwise result in uptoupto 30% increase in Air/Fuel mixture richness in the engine. Purge 30% increase in Air/Fuel mixture richness in the engine. Purge control valve is situated in control valve is situated in the pipe line that connects the intake manifold of the engine tothe pipe line that connects the intake manifold of the engine to the charcoal canister.the charcoal canister.

Control of the purge valve must allow for two criteria: Control of the purge valve must allow for two criteria: There must be enough vapor flow so that charcoal canister does nThere must be enough vapor flow so that charcoal canister does not become saturated and leak fuel vapors into the ot become saturated and leak fuel vapors into the atmosphere.atmosphere.Purge flow must generally occur under lambda closedPurge flow must generally occur under lambda closed--loop control so that the effect of the purge vapors on A/F ratioloop control so that the effect of the purge vapors on A/F ratio can can be detected and the fuel metering corrected.be detected and the fuel metering corrected.

When the PCM commands the purge valve to meter vapor from the When the PCM commands the purge valve to meter vapor from the canister, it requests a duty cycle (ratio of ON time to OFF canister, it requests a duty cycle (ratio of ON time to OFF time). This allows the amount of vapor flow to be regulated depetime). This allows the amount of vapor flow to be regulated depending on the engine operating conditions. When lambda nding on the engine operating conditions. When lambda control is not operating, during coldcontrol is not operating, during cold--start, only low dutystart, only low duty--cycles and therefore, small amount of purge vapors, are allowed cycles and therefore, small amount of purge vapors, are allowed into into the intake manifold. Under deceleration fuel cut off, the purge the intake manifold. Under deceleration fuel cut off, the purge valve is closed entirely to minimize the possibility of unburnedvalve is closed entirely to minimize the possibility of unburnedHCsHCs in the exhaust.in the exhaust.The OBD II diagnostic system shall control the air flow of the cThe OBD II diagnostic system shall control the air flow of the complete evaporative system. In addition , the diagnostic system omplete evaporative system. In addition , the diagnostic system shall also monitor the complete evaporative system for the emissshall also monitor the complete evaporative system for the emission of HC vapor into the atmosphere by performing a pressure ion of HC vapor into the atmosphere by performing a pressure or vacuum check of the complete evaporative system. From time toor vacuum check of the complete evaporative system. From time to time, manufacturers may occasionally turn off the time, manufacturers may occasionally turn off the evaporative purge system in order to carry out a check. evaporative purge system in order to carry out a check. The following is the procedure: At idle position, the canister pThe following is the procedure: At idle position, the canister purge valve is activated, and the lambda controller is monitored urge valve is activated, and the lambda controller is monitored for for its reaction. its reaction.

A pressure sensor in the fuel tank would provide a pressure pA pressure sensor in the fuel tank would provide a pressure profile which will determine if a leak existed in the system. rofile which will determine if a leak existed in the system. For leak detection of the evaporative system, a valve instalFor leak detection of the evaporative system, a valve installed at the atmospheric side of the canister which is the output led at the atmospheric side of the canister which is the output to the to the

active carbon filter is shut off and the canister pressure is deactive carbon filter is shut off and the canister pressure is decreased to about creased to about --1.51.5 KPaKPa. The complete system is turned off and the . The complete system is turned off and the pressure within the canister is monitored for variation with timpressure within the canister is monitored for variation with time. The pressure gradient, together with other parameters like the. The pressure gradient, together with other parameters like the e amount of fuel, will indicate possible leaks. If a leak is detecamount of fuel, will indicate possible leaks. If a leak is detected the MIL is illuminated. The complete test suite is more ted the MIL is illuminated. The complete test suite is more elaborate and is described in detail in a later section.elaborate and is described in detail in a later section.

EGR System Monitoring:EGR System Monitoring: During overrun and heavy load of the vehicle the peak combustioDuring overrun and heavy load of the vehicle the peak combustion temperature of n temperature of the cylinders of the engine will increase to more than 3000the cylinders of the engine will increase to more than 3000o o F. A measured quantity of exhaust gas is F. A measured quantity of exhaust gas is introduced into intake manifold via aintroduced into intake manifold via a pintlepintle valve connecting the exhaust gas to the intake manifold. By valve connecting the exhaust gas to the intake manifold. By mixing a portion of the exhaust gas with fresh intake air/fuel mmixing a portion of the exhaust gas with fresh intake air/fuel mixture the oxygen content is reduced without ixture the oxygen content is reduced without reducing the mass of gas processed by the cylinder. The engine areducing the mass of gas processed by the cylinder. The engine acts partially like an external combustion cts partially like an external combustion engine in that the combustion process must impart energy to the engine in that the combustion process must impart energy to the inert exhaust gas as well as to the air charge. inert exhaust gas as well as to the air charge. The net effect is to reduce the flame temperature at part load wThe net effect is to reduce the flame temperature at part load while retaining the power of the engine. The hile retaining the power of the engine. The reduction of temperature reducesreduction of temperature reduces NOxNOx emission produced by the engine.emission produced by the engine.The OBD II diagnostic has to monitor theThe OBD II diagnostic has to monitor the pintlepintle valve, and the amount of exhaust gas delivered by thevalve, and the amount of exhaust gas delivered by the pintlepintlevalve. The correct amount of exhaust gas is obtained from predefvalve. The correct amount of exhaust gas is obtained from predefined engine RPM/load (MAP) table showing ined engine RPM/load (MAP) table showing optimum EGR valve openings & gas amount, engine coolant temperatoptimum EGR valve openings & gas amount, engine coolant temperature, manifold absolute pressure (MAP) ure, manifold absolute pressure (MAP) pressure, and engine RPM. During EGR operation, the fuel is cut pressure, and engine RPM. During EGR operation, the fuel is cut off. The OBD II diagnostic consists of several off. The OBD II diagnostic consists of several algorithms to monitor all the functions listed above. EGRalgorithms to monitor all the functions listed above. EGR pintlepintle valve position is monitored by the PCM for valve position is monitored by the PCM for proper opening. The amount of exhaust gas ingested is monitored proper opening. The amount of exhaust gas ingested is monitored from the EGRfrom the EGR pintlepintle valve flow rate, and valve flow rate, and the time of the valve opening. This amount is compared with the the time of the valve opening. This amount is compared with the required amount obtained from the table required amount obtained from the table with predefined values. If there is a significant difference betwith predefined values. If there is a significant difference between the actual and the needed values, the EGR ween the actual and the needed values, the EGR malfunction is detected. Engine coolant temperature is monitoredmalfunction is detected. Engine coolant temperature is monitored for an increase in value during EGR for an increase in value during EGR operation. MAP pressure is monitored for increase in pressure doperation. MAP pressure is monitored for increase in pressure during EGR operation. Finally the Engine uring EGR operation. Finally the Engine RPM (900 RPM (900 -- 1100) is monitored for a decrease of about 50 RPM during EGR (D1100) is monitored for a decrease of about 50 RPM during EGR (DTC for fault is P0401 for no TC for fault is P0401 for no decrease in RPM when vehicle speed is 25 MPH with brakes applieddecrease in RPM when vehicle speed is 25 MPH with brakes applied) operation. ) operation.

OBD(II)In addition the electrical characteristics of theIn addition the electrical characteristics of the pintlepintle valve are checked, including the voltage, the current drawn by valve are checked, including the voltage, the current drawn by the movingthe moving pintlepintle, and the circuit continuity including open circuit as well as s, and the circuit continuity including open circuit as well as short circuit in the wiring. There are hort circuit in the wiring. There are two methods used in verifying that EGR is functioning properly mtwo methods used in verifying that EGR is functioning properly meaning no sticking valve or clogged EGR passage. eaning no sticking valve or clogged EGR passage. The first method is to intentionally open the EGR valve through The first method is to intentionally open the EGR valve through a measured value during normal operation when a measured value during normal operation when there is no need for EGR and measure the response of critical sthere is no need for EGR and measure the response of critical system parameters due to this perturbation namely, ystem parameters due to this perturbation namely, Engine RPM, coolant temperature, MAP pressure,Engine RPM, coolant temperature, MAP pressure, pintlepintle valve position, and closedvalve position, and closed--loop fuel system correction. If loop fuel system correction. If the critical parameters do not conform to the desired values EGRthe critical parameters do not conform to the desired values EGR malfunction is indicated. The second method is to malfunction is indicated. The second method is to wait for the condition of the vehicle when the EGR is operated wait for the condition of the vehicle when the EGR is operated by the PCM as a consequence of engine overrun or by the PCM as a consequence of engine overrun or high load. Then intentionally disable EGR operation for a small high load. Then intentionally disable EGR operation for a small predefined amount of time and measure the critical predefined amount of time and measure the critical parameters. If the difference in critical parameter values do noparameters. If the difference in critical parameter values do not conform to the expected values then EGR t conform to the expected values then EGR malfunction is indicated.malfunction is indicated.A much simpler algorithm measures the increase in coolant temperA much simpler algorithm measures the increase in coolant temperature during EGR and if the increase in not ature during EGR and if the increase in not within desired range EGR malfunction is indicated. In addition iwithin desired range EGR malfunction is indicated. In addition increase in manifold absolute pressure (MAP) ncrease in manifold absolute pressure (MAP) during EGR and if the increase is not within desired range EGR mduring EGR and if the increase is not within desired range EGR malfunction is indicated. alfunction is indicated. Due to uncertainties encountered in EGR monitoring, more than onDue to uncertainties encountered in EGR monitoring, more than one diagnostic is necessary before a fault code is e diagnostic is necessary before a fault code is stored and the MIL is illuminated. One method is to requires thrstored and the MIL is illuminated. One method is to requires three successive tests, each revealing an EGR fault, ee successive tests, each revealing an EGR fault, before a fault code is stored. If a test reveals no fault , the before a fault code is stored. If a test reveals no fault , the next test is performed eleven minutes later. The predefined next test is performed eleven minutes later. The predefined operating condition is deceleration which means that the test isoperating condition is deceleration which means that the test is performed during deceleration of the vehicle. performed during deceleration of the vehicle. Different frequencies of testing are also used in the diagnosticDifferent frequencies of testing are also used in the diagnostic. Another method requires eight tests to be performed . Another method requires eight tests to be performed within a two minute period before a fault code is stored when twwithin a two minute period before a fault code is stored when two failures occur within that period. Currently about o failures occur within that period. Currently about fifty percent of the manufacturers monitor the EGR passage tempefifty percent of the manufacturers monitor the EGR passage temperature, twentyrature, twenty--five percent monitor the EGR valve five percent monitor the EGR valve signal (position), and twentysignal (position), and twenty--five percent use the intrusive perturbation method to detect EGRfive percent use the intrusive perturbation method to detect EGR malfunction. malfunction. The legal OBD II requirement is: The diagnostic system shall monThe legal OBD II requirement is: The diagnostic system shall monitor the EGR system on vehicle for low and high itor the EGR system on vehicle for low and high flow rate malfunction. flow rate malfunction. The hardware failure code of P1406 is set for out of range voltThe hardware failure code of P1406 is set for out of range voltage signal from theage signal from the pintlepintle valve position sensor of valve position sensor of more than 10% from commanded value. more than 10% from commanded value. Another manufacturer monitors the exhaust gas pressures on both Another manufacturer monitors the exhaust gas pressures on both sides of an orifice in the passage to the EGR sides of an orifice in the passage to the EGR valve. The pressure drop across the orifice is measured as the evalve. The pressure drop across the orifice is measured as the exhaust gas flows through the orifice. If the pressure xhaust gas flows through the orifice. If the pressure differential is not within permissible limits, EGR fault code isdifferential is not within permissible limits, EGR fault code is set. set. DifferentDifferent DTCsDTCs are set for tests performed with similar EGR diagnostic objectare set for tests performed with similar EGR diagnostic objectives due to differences in test time, and ives due to differences in test time, and critical parameter values. critical parameter values. EGR diagnostics diagnostics are described in more detail in a laEGR diagnostics diagnostics are described in more detail in a later section.ter section.

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Secondary Air System Monitoring:Secondary Air System Monitoring: Secondary air system is used to improve the performance of the Secondary air system is used to improve the performance of the catalytic converter (Three way) by providing extra catalytic converter (Three way) by providing extra oxygen rich air to either the converter itself or to the exhaustoxygen rich air to either the converter itself or to the exhaust manifold. The catalyst temperature must be above about 200manifold. The catalyst temperature must be above about 200o o C to efficiently oxidize HC and C to efficiently oxidize HC and reducereduce NOxNOx. During engine warm. During engine warm--up when the catalytic converter is cold, HC and CO are oxidized up when the catalytic converter is cold, HC and CO are oxidized in the exhaust manifold by routing secondary air to in the exhaust manifold by routing secondary air to the exhaust manifold in controlled quantify by the PCM. This crethe exhaust manifold in controlled quantify by the PCM. This creates extra heat to speed warmates extra heat to speed warm--up of the converter and EGO sensor, enabling the PCM to up of the converter and EGO sensor, enabling the PCM to go into closedgo into closed--loop mode more quickly.loop mode more quickly.During openDuring open--loop control (cold converter) the converter is liable to be damaloop control (cold converter) the converter is liable to be damaged if excessive heat is applied to it, to warm it up. This can ged if excessive heat is applied to it, to warm it up. This can happen if happen if excessive amounts of HC and CO are oxidized in the exhaust manifexcessive amounts of HC and CO are oxidized in the exhaust manifold during periods of heavy loads which call for fuel enrichmentold during periods of heavy loads which call for fuel enrichment, or during severe , or during severe deceleration. During startdeceleration. During start--up and such heavy loads, the secondary air is not let into exhauup and such heavy loads, the secondary air is not let into exhaust manifold but directed into the air cleaner where it has no st manifold but directed into the air cleaner where it has no effect on exhaust temperatures.effect on exhaust temperatures.After warmAfter warm--up, during closedup, during closed--loop operation, the secondary air is used to supply oxygen to thloop operation, the secondary air is used to supply oxygen to the second chamber of the threee second chamber of the three--way catalyst, in dualway catalyst, in dual--chamber converter system. In a dualchamber converter system. In a dual--chamber converter, the first chamber contains rhodium, palladiumchamber converter, the first chamber contains rhodium, palladium, and platinum to reduce, and platinum to reduce NOxNOx and to oxidize HC and to oxidize HC and CO. The second chamber contains only platinum and palladium.and CO. The second chamber contains only platinum and palladium. The extra oxygen from the secondary air improves the converter’The extra oxygen from the secondary air improves the converter’s ability to oxidize s ability to oxidize HC and CO in the second converter chamber. The control of the seHC and CO in the second converter chamber. The control of the secondary air is done by using two solenoid valves similar to the condary air is done by using two solenoid valves similar to the EGREGR pintlepintle valve. One valve. One valve switches air flow to the exhaust manifold or to the air clvalve switches air flow to the exhaust manifold or to the air cleaner (atmosphere). The other valve switches air flow to the exheaner (atmosphere). The other valve switches air flow to the exhaust manifold or to the aust manifold or to the catalytic converter. The air routing is controlled based on engicatalytic converter. The air routing is controlled based on engine coolant temperature and Air/Fuel ratio, indicated by the lambne coolant temperature and Air/Fuel ratio, indicated by the lambda sensor. If the control is da sensor. If the control is openopen--loop and if the coolant temperature is below threshold and Air/Floop and if the coolant temperature is below threshold and Air/Fuel ratio is not too rich, then the air flow is directed to the uel ratio is not too rich, then the air flow is directed to the exhaust manifold. If exhaust manifold. If coolant temperature is higher than threshold and the Air/Fuel racoolant temperature is higher than threshold and the Air/Fuel ratio is rich (lambda < 1) then the secondary air is directed totio is rich (lambda < 1) then the secondary air is directed to the air cleaner which exits the air cleaner which exits to the atmosphere. If the control is closedto the atmosphere. If the control is closed--loop, then the lambda sensor is monitored for correlated deviatiloop, then the lambda sensor is monitored for correlated deviations when the secondary air flow is changed ons when the secondary air flow is changed from exhaust manifold, or catalytic converter, or air cleaner, dfrom exhaust manifold, or catalytic converter, or air cleaner, depending on coolant temperature, and lambda value. The OBD II reepending on coolant temperature, and lambda value. The OBD II requirement is that the quirement is that the secondary air system shall have the diagnostic system monitor thsecondary air system shall have the diagnostic system monitor the proper functioning of the secondary air delivery, and any air e proper functioning of the secondary air delivery, and any air switching valve switching valve (solenoid). (solenoid). The critical parameters of the secondary air system are monitoreThe critical parameters of the secondary air system are monitored and if found to be out of permissible range of values, the faud and if found to be out of permissible range of values, the fault code is set. The MIL is lt code is set. The MIL is illuminated. illuminated. Secondary air diagnostics are described in more detail in a lateSecondary air diagnostics are described in more detail in a later section.r section.

Comprehensive Components Monitoring includes all the sensors, soComprehensive Components Monitoring includes all the sensors, solenoids, fuel injectors, fuel pump, ignition coil, actuators lenoids, fuel injectors, fuel pump, ignition coil, actuators (valves), and the associated wiring, ground, and power supply. T(valves), and the associated wiring, ground, and power supply. The following components with theirhe following components with their DTCsDTCs are described are described below:below:uuManifold absolute pressure (MAP) sensorManifold absolute pressure (MAP) sensor DTCsDTCs 105 105 -- 109 109 uu Intake air temperature sensorIntake air temperature sensor DTCsDTCs 110110--114114uuOxygen sensor sensorOxygen sensor sensor DTCsDTCs 130 130 --167167uuMass air flow (MAF) sensorMass air flow (MAF) sensor DTCsDTCs 100100--104104uuThrottle position sensorThrottle position sensor DTCsDTCs 120120--124, 220124, 220--229229uuCrankshaft angle sensorCrankshaft angle sensor DTCsDTCs 335335--344, 385344, 385--389389uu Engine coolant temperature sensorEngine coolant temperature sensor DTCsDTCs 115115--119, 125119, 125--126126uuKnock sensorKnock sensor DTCsDTCs 325325--334334uuEngine speed sensorEngine speed sensor DTCsDTCs 320320--323323uuVehicle speed sensorVehicle speed sensor DTCsDTCs 500500--503503uuMisfire (sensor) detectorMisfire (sensor) detector DTCsDTCs 300300--312312uuCanister vent valveCanister vent valve DTCsDTCs 440440--455455uu Purge valvePurge valve DTCsDTCs 465465--469 469 uuIgnition coil (ignition control)Ignition coil (ignition control) DTCsDTCs 350350--379379uuFuel system (fuel metering)Fuel system (fuel metering) DTCsDTCs 170170--195, 230195, 230--233233uuIndividual fuel injectorsIndividual fuel injectors DTCsDTCs 251251--296296uuEGR sensor/ valveEGR sensor/ valve DTCsDTCs 400400--408408uuIdle air control (IAC) valveIdle air control (IAC) valve DTCsDTCs 505505--507507uuSecondary air valveSecondary air valve DTCsDTCs 410410--419419uuFuel level sensorFuel level sensor DTCsDTCs 460460--464464uuCatalytic converterCatalytic converter DTCsDTCs 420420--434

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434

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The OBD II diagnostics consist of conducting The OBD II diagnostics consist of conducting tests on all the sensors and actuators listed tests on all the sensors and actuators listed above. The nature of these tests is above. The nature of these tests is described below. If any fault is detected in described below. If any fault is detected in any of the tests of these devices including , any of the tests of these devices including , sensor or actuator component, electrical sensor or actuator component, electrical circuit, wiring, and power source, the circuit, wiring, and power source, the corresponding diagnostic trouble code corresponding diagnostic trouble code (DTC) assigned in SAE J 2120 to that fault, (DTC) assigned in SAE J 2120 to that fault, is displayed and the malfunction is displayed and the malfunction indication light (MIL)is illuminated. indication light (MIL)is illuminated.

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SAE J 2012 standardSAE J 2012 standard defines thedefines the recommended practice for diagnostic trouble codes (DTC) of recommended practice for diagnostic trouble codes (DTC) of all comprehensive components listed above. The DTC consists of all comprehensive components listed above. The DTC consists of an alphaan alpha--numericnumericdesignator p0 designator p0 -- p3 forp3 for powertrainpowertrain, where p0 codes belong to SAE controlled codes, P1 belong to , where p0 codes belong to SAE controlled codes, P1 belong to manufacturer, and the rest are reserved for future use. The P0 cmanufacturer, and the rest are reserved for future use. The P0 codes are followed by three digit odes are followed by three digit codes assigned to individual faults. The assignment of the propecodes assigned to individual faults. The assignment of the proper designator should be r designator should be determined by the PCM. In case of ambiguity, the upper most nibbdetermined by the PCM. In case of ambiguity, the upper most nibble of the two le of the two --byte code byte code message as defined in SAE J 1979 will define the source system amessage as defined in SAE J 1979 will define the source system as follows: P0 s follows: P0 -- 0000, and P1 0000, and P1 --0001. This standard defines diagnostic trouble codes for all the0001. This standard defines diagnostic trouble codes for all the circuits, components, and circuits, components, and systems which are controlled by SAE, namely P0 codes. The P0 codsystems which are controlled by SAE, namely P0 codes. The P0 codes are defined by four es are defined by four different categories: General Circuit Malfunction, Range/Performdifferent categories: General Circuit Malfunction, Range/Performance Problem, Low Circuit ance Problem, Low Circuit Input, and High Circuit Input. Manufacturers can define specificInput, and High Circuit Input. Manufacturers can define specific DTCsDTCs to meet their controller to meet their controller algorithms, but all DTC words must meet the terms’ definitions salgorithms, but all DTC words must meet the terms’ definitions specified in SAE J 1930 pecified in SAE J 1930 standard for Diagnostic terms, definitions, abbreviations, and astandard for Diagnostic terms, definitions, abbreviations, and acronyms. The definition of these cronyms. The definition of these four categories of faults will be described first. Then thefour categories of faults will be described first. Then the DTCsDTCs for different faults for each for different faults for each sensor and actuator listed above will be described. SAE J 2012 sensor and actuator listed above will be described. SAE J 2012 provides guidance (definitions) provides guidance (definitions) for message formats, Parameter Identification numbers (for message formats, Parameter Identification numbers (PIDsPIDs) and their definitions with actual ) and their definitions with actual examples for compliance. The main aspects of these definitions aexamples for compliance. The main aspects of these definitions are covered below. For more re covered below. For more detailed knowledge of thedetailed knowledge of the DTCsDTCs and their messages, please refer to SAE J 2012, SAE J 1979, andand their messages, please refer to SAE J 2012, SAE J 1979, andSAE J 1930. SAE J 1930.

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General Circuit Malfunction: This is a general purpose failure resulting in the component not responding with expected value or any value. This could be due to short circuit in the circuit wiring, or an open circuit, or a complete break down of the function resulting in a wrong response including no response.

Range/Performance: This is the case when the component is functional in general terms except that the response value is not within the normal operating range. This can be due to stuck at 0 or stuck at 1 fault, or erratic, intermittent, or skewed values indicating poor performance of the circuit, component, or system.

Low Circuit Input: The circuit voltage, frequency or other signal measured at the controlmodule input terminal or Pin is at or near zero. This is measured with the external circuit,component, or system connected. The signal type (voltage, frequency) shall be included inthe message in place of the word “input”.

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High Circuit Input: The circuit voltage, frequency or other signal measured at the controlmodule input terminal or Pin is at or near full scale. This is measured with the external circuit,component, or system connected. The signal type (voltage, frequency) shall be included inthe message in place of the word”input”.

DTC codes are grouped in different categories. Each category has 100 codes assigned to itas follows: P01 - Fuel and Air metering 100-199, P02 - Fuel and Air metering,

P03 - Ignition system or Misfire 300-389, P04 - auxiliary emission controls 400 - 485, and P05 - vehicle speed, idle control, and auxiliary inputs 500 - 574, P06 - Computer and auxiliary outputs 600- 605, and P07 Transmission 700 - 790.

Since OBD II focuses on emissions control only DTCs upto P04 followed by three digit fault code are covered here.DTCs are defined to indicate a suspected trouble or problem area and are intended as a directive to the proper service procedure. DTC s should not be used to indicate theabsence of problems but only to indicate specific fault. The decision to illuminate MIL for any DTC is manufacture specific based on their testing of how each system malfunction affects emissions.

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Core DTCS: Core DTCs are those codes which have achieved compliance uniformlythroughout the industry. For these, a common DTC number, and fault message is assigned.Undefined DTCs are reserved for future use. Even though the service procedures for rectifying each of these DTCs may vary among manufacturers, the fault indicated by the DTC is common enough to be assigned a particular fault code.

Non-Uniform DTC: These are fault codes that have very little commonality among manufacturers due to system differences, implementation differences, or diagnosticstrategy differences. Manufacturers who define their own DTCs in this area areurged to remain consistent across their product line when assigning codes in manufacturercontrolled area. Same groupings should be used as in SAE controlled area, i.e.., 100s and 200sfor fuel and air metering, 300 for ignition system or misfire, etc.

Each defined DTC is assigned a message to indicate the circuit, component, or system areathat is faulty. The messages are organized such that different messages related to a

particular sensor or system are grouped together. In cases where there are various faultmessages for different types of faults, the group also has a “Generic” message as the fault Code/Message of the group. Manufacturer has a choice to use the specific or generic faultcode, provided only one code is used consistently to describe that fault.

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In a case where messages are broken down into more specific fault descriptions for acircuit, component, or system, as is done in complex cases, the manufacturer should

choose the fault code most applicable to their diagnosable fault. The messages are intended to allow the manufacturers to use them as often as possible yet still not conflict with their specific repair procedures. Each code should lead to a specific repair procedure(s).

Examples: As a guide to clarify the above points a few examples are given. For manufacturers choosing to implement basic diagnostics that provide generalfault information but depend on service procedures and Off-board diagnostics toisolate the problem, general circuit, component, and system codes will be used.

For example, if a fault is detected in in the throttle position sensor circuit, instead of burdening the OBD II with determining the specific type of fault, a Code P0120 would be stored indicating some type of problem with that circuit. The serviceprocedure would then allow the service technician to determine the type of fault and the specific location of the fault. On these types of systems, such as sensors, actuators, coils, and switches, a shorted sensor input, an open sensor input, and even

out of range sensor output would all set the same fault code.

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However, manufacturers choosing to allow the OBD II to better isolate the fault to specificcause would not use the general fault code/message, but would use the more specific

code/message associated with the particular circuit, component, or system.For example, in diagnosing a 5 volt reference throttle position sensor, if the input signal at the PCM is stuck at near 0 volt, the manufacturer has the choice to select either of two codes:P0120 (general malfunction), or P0122 (specific low circuit input ), depending on the

manufacturer’s diagnostic procedures. The root cause of this fault can be any one of electricalor mechanical problems. Identification of the root cause is done using the diagnosticprocedures and is not implied by the DTC message, thus allowing the manufacturer the

flexibility in assigning DTCs.The powertrain control strategies in performing OBD II diagnostics depend on each manufacturer who has considerable flexibility as to how the diagnostics are implementedprovided the above guidelines of SAE J 2012, SAE 1979, and SAE J 1930 are complied with.A typical use of OBD II procedure is given below as a generic example:The diagnostic mode is entered by switching on the ignition and then simultaneously depressing the OFF and Warmer buttons on the climate control system (cadillac).

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The fault codes are displayed by flashing the “Check Engine” light and entering the display mode. Each fault code is displayed in sequence starting with the code that checks that all display segments are working correctly. After verifying that all display segments are working, the fault codes for all component failures are displayed in sequence, beginning with the lowest and proceeding to the highest code. The mechanic notes the fault codes that are displayed , and using a reference manual, identifies the failed components. The fault codes must comply with the SAE J 2012 standard. After all fault codes are displayed, special code appearson the display indicating the end of display, and the engine control system awaitsfurther action by the mechanic.

Typically the “check engine” light on the instrument panel is illuminated whenever any fault occurs. For emissions related faults the MIL light will not go out until cleared frommemory by the mechanic. For non-emissions related faults the MIL light goes outautomatically if the malfunction clears. However the PCM stores the DTC associated with the detected failure until the diagnostic system is manually cleared oruntil a specified number of engine cycles (twenty) occur with no malfunction. Forsome DTCs (of lesser consequence) there is no activation of the “check engine” MIL light.

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whenever a defect occurs the mechanic must follow a specific procedure to isolate the particular problem. These procedures are outlined in the shop manuals. An example procedure will be illustrated for an Oxygen sensor fault, P0130 which indicates the sensor circuit malfunction. If you recall from the Oxygen sensor behaviordescribed earlier, the O2 sensor switches between 0 (100 mv) and 1 volt (900 mv) as the A/F mixture switches between the extreme conditions of lean and rich . Recall alsothat this voltage swing requires that the O2 must be at a temperature above 2000 C.

The voltage of cold O2 sensor is about 0.5 volt with a bias of 0.45 Volt and the electronic control system will not go into closed-loop operation when O2 is cold.Possible causes of fault code P0130 include:

O2 sensor is not functioning correctlyCircuit wiring is defective ( stuck at some value)The control (circuit) unit processing O2 sensor signal is not functioning properly

Further investigation is required to attempt to isolate the specific problem.To check the operation of the O2 sensor , the average value of its output voltage is measured using the OBD II procedure which will be explained presently.

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The desired voltage is displayed on the Instrument panel (IP) in multiples of 1/100 volt.Thus to say , “00” corresponds to 0 volts and “99” corresponds to 0.99 volt, etc.Using this voltage, the mechanic follows the following procedure: If the O2 sensor voltageis less than 0.37volt and more than 0.57 volt, the mechanic is directed by the procedureto investigate the circuit wiring of the O2 sensor for defects. If the O2 sensor voltage is between 0.37 volt and 0.57 volt tests are performed to determine whether O2 sensor or the control (circuit) unit processing the O2 sensor signal is faulty.

The mechanic can then jumper the input leads together at the input to the control unit,simulating a O2 sensor short circuit, and must read the sensor voltage value using the

OBD II display procedure. If this voltage is less than 0.05 volt, the control unit isfunctioning correctly and the O2 sensor must be investigated for defects. If the indicated sensor voltage is greater than 0.05 volt, the control unit is faulty and should be replaced.

when diagnosing a problem, the mechanic might wish to clear a fault code from the PCMmemory. A good reason to do this can be to test whether the failure is “hard” or

intermittent. To clear DTC the mechanic pushes “OFF” and “HI” buttons on IP simultaneously until “00” is displayed on IP.

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After all fault codes are cleared, the mechanic has several choices of test modes including:♦ Request current powertrain diagnostic data (mode $01)♦ Request current powertrain Freeze Frame” data (mode $02)♦ Request Emission related DTCs♦ Request OBD II test results of continuously

monitored / non-continuously monitored systems♦ Request control of OBD II system.

Mode $01: The purpose of this mode is to allow access to current emission related data values. The request for information includes a Parameter Identification(PID) value that indicates to OBD II the specific information requested. PID definition, scaling information, and display formats are included in SAE J 1979. for compliance.The OBD II module will respond to this message by transmitting the requested data value last determined by the PCM. All data values returned for sensor readings will be actual readings, not default or substitute values used by the PCM because of a fault with that sensor.. Not all PIDs are applicable or supported by all systems. PID $00 is a bit encoded PID that indicates, for each module, which PIDs that module supports. PID $00 must be supported by all modules that respond to a Mode $01 request as defined in the standard SAE J 1979, because tools that conform to SAE J 1978 use this request to determine the protocol information supported for OBD II communications.

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For more detailed information on all the request modes that you can use to perform OBD II diagnostics using OBD II communications, and Scan Tool (SAE J 1978) , refer tothe HS -3000 SAE standards manual. The powertrain control strategies to perform OBD II diagnostics in general are described so far. Now the specific diagnostics performed for DTCs of the sensors, actuators, and systemsindicated below will be briefly described.

Manifold absolute pressure (MAP) sensor (Manifold absolute pressure (MAP) sensor (DTCsDTCs 105 105 -- 109): 109): MAP sensor diagnostics areMAP sensor diagnostics areperformed for deterioration ofperformed for deterioration of piezoresisterpiezoresister or capacitor characteristics. In case of electricalor capacitor characteristics. In case of electricalcircuit malfunction fault code 105 is assigned. If the sensor circuit malfunction fault code 105 is assigned. If the sensor is indicating out of range reading fault is indicating out of range reading fault code 106 is assigned. If the sensor is indicating very low readcode 106 is assigned. If the sensor is indicating very low reading fault code 107 is assigned. If the ing fault code 107 is assigned. If the sensor is indicating very high reading fault code 108 is assigsensor is indicating very high reading fault code 108 is assigned. The expected value is estimated ned. The expected value is estimated using mass air flow sensor reading and engine parameters. If tusing mass air flow sensor reading and engine parameters. If the sensor is indicating he sensor is indicating intermittent faulty reading, fault code 109 is assigned. intermittent faulty reading, fault code 109 is assigned.

Intake air temperature (IAT) sensor (Intake air temperature (IAT) sensor (DTCsDTCs 110110--114): 114): IAT sensor diagnostics are performed for IAT sensor diagnostics are performed for deterioration ofdeterioration of thermisterthermister characteristics. In case ofcharacteristics. In case of thermisterthermister circuit malfunction fault code 110 circuit malfunction fault code 110 is assigned. If the sensor is indicating out of range reading is assigned. If the sensor is indicating out of range reading fault code 111 is assigned. The fault code 111 is assigned. The expected value is estimated using coolant temperature sensor rexpected value is estimated using coolant temperature sensor reading and engine parameters. If eading and engine parameters. If the sensor is indicating very low reading fault code 112 is athe sensor is indicating very low reading fault code 112 is assigned. If the sensor is indicating ssigned. If the sensor is indicating very high reading fault code 113 is assigned. If the sensor very high reading fault code 113 is assigned. If the sensor is indicating intermittent faulty is indicating intermittent faulty reading fault code 114 is assigned. reading fault code 114 is assigned.

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Oxygen Sensor (OOxygen Sensor (O2 ) 2 ) Sensor Sensor (( DTCsDTCs 130130--167): 167): OO22 sensor diagnostics are sensor diagnostics are performed to check deterioration of electrochemical pumping actperformed to check deterioration of electrochemical pumping action that ion that generates voltage sensitivity to the oxygen density in the exhaugenerates voltage sensitivity to the oxygen density in the exhaust st manifold. In case ofmanifold. In case of ZirconiaZirconia electrode circuit malfunction fault code 130 electrode circuit malfunction fault code 130 is assigned. If the Ois assigned. If the O22 sensor is indicating slow response fault code 133 is sensor is indicating slow response fault code 133 is assigned. The expected value is estimated using closedassigned. The expected value is estimated using closed--loop frequency loop frequency and engine parameters. If the Oand engine parameters. If the O22 sensor is indicating very low voltage sensor is indicating very low voltage fault code 131 is assigned. If the Ofault code 131 is assigned. If the O22 sensor is indicating very high sensor is indicating very high voltage fault code 132 is assigned. If the Ovoltage fault code 132 is assigned. If the O22 sensor is indicating no sensor is indicating no activity, fault code 134 is assigned. In case of Oactivity, fault code 134 is assigned. In case of O22 sensor heater circuit sensor heater circuit malfunction fault code 135 is assigned. The other codes from 13malfunction fault code 135 is assigned. The other codes from 135 to 167 5 to 167 are assigned to similar faults for other Oare assigned to similar faults for other O22 sensors and heaters in other sensors and heaters in other catalytic converters in the system. Oxygen sensor diagnostics acatalytic converters in the system. Oxygen sensor diagnostics are re described in detail in alter section.described in detail in alter section.

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Mass air flow (MAF) sensor (DTC 100Mass air flow (MAF) sensor (DTC 100--104): 104): MAF sensor diagnostics are performed for deterioration of elMAF sensor diagnostics are performed for deterioration of electrical ectrical and resister characteristics. In case of electrical circuit mand resister characteristics. In case of electrical circuit malfunction alfunction fault code 100 is assigned. fault code 100 is assigned. If the sensor is indicating out of range 1reading fault code 1If the sensor is indicating out of range 1reading fault code 101 is 01 is assigned. If the sensor is indicating very low reading fault cassigned. If the sensor is indicating very low reading fault code 102 is ode 102 is assigned. If the sensor is indicating very high reading faultassigned. If the sensor is indicating very high reading fault code 103 is code 103 is assigned. The expected value is estimated using MAP sensor reaassigned. The expected value is estimated using MAP sensor reading ding and engine parameters. If the sensor is indicating intermittand engine parameters. If the sensor is indicating intermittent faulty ent faulty reading fault code 104 is assigned.reading fault code 104 is assigned.

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Throttle positionThrottle position Sensor (TPS)Sensor (TPS) (( DTCsDTCs 120120--124, 220124, 220--229):229):TP sensor diagnostics are performed for deterioration of potenTP sensor diagnostics are performed for deterioration of potentiometer operatedtiometer operatedswitch A circuit characteristics. In case of switch A circuit mswitch A circuit characteristics. In case of switch A circuit malfunctionalfunctionfault code 120 is assigned. If the switch A circuit is indifault code 120 is assigned. If the switch A circuit is indicating out of range cating out of range reading fault code 121 is assigned. If the switch A circuit reading fault code 121 is assigned. If the switch A circuit is indicating very low is indicating very low reading fault code 122 is assigned. If the switch A circuit reading fault code 122 is assigned. If the switch A circuit is indicating very high is indicating very high reading fault code 123 is assigned. The expected value is estireading fault code 123 is assigned. The expected value is estimated using air flow mated using air flow sensor reading and engine parameters. If the switch A circuitsensor reading and engine parameters. If the switch A circuit is indicating is indicating intermittent faulty reading fault code 124 is assigned. For swintermittent faulty reading fault code 124 is assigned. For switch B circuit , faultitch B circuit , faultcodes 220codes 220--224 are set for identical faults listed above. For switch C cir224 are set for identical faults listed above. For switch C circuit , faultcuit , faultcodes 225codes 225--229 are set for identical faults listed above.229 are set for identical faults listed above.

Crankshaft Angular Position Sensor (Crankshaft Angular Position Sensor ( DTCsDTCs 335335--344, 385344, 385-- 389): 389): Crankshaft angular position sensor diagnostics are performed Crankshaft angular position sensor diagnostics are performed for deterioration of magnetic reluctance of sensor A circuit for deterioration of magnetic reluctance of sensor A circuit characteristics. In case of sensor A circuit malfunction faultcharacteristics. In case of sensor A circuit malfunction faultcode 335 is assigned. If the sensor A circuit is indicating ocode 335 is assigned. If the sensor A circuit is indicating oututof range reading fault code 336 is assigned. If the sensor A of range reading fault code 336 is assigned. If the sensor A circuit is indicating very low reading fault code 337 is acircuit is indicating very low reading fault code 337 is assigned. ssigned. If the sensor A circuit is indicating very high reading If the sensor A circuit is indicating very high reading fault code 338 is assigned. The expected value is estimated fault code 338 is assigned. The expected value is estimated using engine speed another engine parameters. using engine speed another engine parameters. If the sensor A circuit is indicating intermittent faulty readIf the sensor A circuit is indicating intermittent faulty reading faulting faultcode 339 is assigned. For sensor C circuit , faultcode 339 is assigned. For sensor C circuit , faultcodes 34 0codes 34 0--344 are set for identical faults listed above. 344 are set for identical faults listed above. For sensor B circuit , fault codes 385For sensor B circuit , fault codes 385--389 are set for 389 are set for identical faults listed above. identical faults listed above.

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Fundamentals ofFundamentals of PowertrainPowertrainControl strategies & OBD II Control strategies & OBD II DiagnosticsDiagnostics

Engine Coolant Engine Coolant Temperature Sensor Temperature Sensor (( DTCsDTCs 115115--119, 125119, 125--126):126):Engine Coolant Temperature sensor diagnostics areEngine Coolant Temperature sensor diagnostics areperformed for deterioration ofperformed for deterioration of thermister thermister characteristics. In case ofcharacteristics. In case of thermisterthermister

and electrical circuit malfunction fault code 115 is assigned. and electrical circuit malfunction fault code 115 is assigned. If the sensor circuit is indicating out of range reading fault If the sensor circuit is indicating out of range reading fault code 116 is assigned. code 116 is assigned. If the sensor circuit is indicating very low reading fault codeIf the sensor circuit is indicating very low reading fault code 117 is assigned. If 117 is assigned. If the sensor circuit is indicating very high reading fault codethe sensor circuit is indicating very high reading fault code 118 is assigned.118 is assigned.The expected value is estimated using engine parameters. If tThe expected value is estimated using engine parameters. If the sensor circuit he sensor circuit is indicating intermittent faulty reading fault code 119 iis indicating intermittent faulty reading fault code 119 is assigned. For s assigned. For insufficient coolant temperature for closed loop fuel control fainsufficient coolant temperature for closed loop fuel control fault code 125 is ult code 125 is assigned. For insufficient coolant temperature for stable operassigned. For insufficient coolant temperature for stable operation fault code ation fault code 126 is assigned. 126 is assigned.

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Knock Sensor (Knock Sensor ( DTCsDTCs 325325--334): 334): Knock sensor diagnostics areKnock sensor diagnostics areperformed for deterioration of piezoelectric or magneto restriperformed for deterioration of piezoelectric or magneto restrictive ctive characteristics. In case of electrical circuit malfunction faulcharacteristics. In case of electrical circuit malfunction fault code 325 is t code 325 is assigned. If the sensor 1 circuit is indicating out of range reassigned. If the sensor 1 circuit is indicating out of range reading ading fault code 326 is assigned. If the sensor 1 circuit is indicfault code 326 is assigned. If the sensor 1 circuit is indicating very low ating very low reading fault code 327 is assigned. If the sensor 1 circuitreading fault code 327 is assigned. If the sensor 1 circuit is indicating is indicating very high reading fault code 328 is assigned. Knocking is detvery high reading fault code 328 is assigned. Knocking is detected by ected by the oscillation frequency of the piezoelectric device or the vothe oscillation frequency of the piezoelectric device or the voltage ltage developed by thedeveloped by the magnetorestrictive magnetorestrictive device when knocking occurs. If device when knocking occurs. If the sensor 1 circuit is indicating intermittent faulty readinthe sensor 1 circuit is indicating intermittent faulty reading fault code g fault code 329 is assigned. 329 is assigned. If the sensor 2 circuit is indicating same faults as listed abovIf the sensor 2 circuit is indicating same faults as listed above, fault codes e, fault codes 330330--3334 are assigned to the respective faults. 3334 are assigned to the respective faults. Knock sensor diagnostics Knock sensor diagnostics are described in detail in a later section.are described in detail in a later section.

Engine Speed Sensor ( DTCs 320-323): Engine speed sensor diagnostics are performed for eterioration of magnetic reluctance characteristics. In case of electrical circuit malfunction fault code 320 is assigned. If the sensor circuit is indicating out of range reading fault code 321 isassigned. If the sensor circuit is indicating no signal , fault code 322 is assigned. The expected value is estimated using engine parameters. If the sensor is indicating intermittent faulty reading, fault code 323 is assigned.

Fundamentals ofFundamentals of PowertrainPowertrainControl strategies & OBD II Control strategies & OBD II DiagnosticsDiagnostics

Fundamentals ofFundamentals of PowertrainPowertrainControl strategies & OBD II Control strategies & OBD II DiagnosticsDiagnostics

Vehicle Speed Sensor ( DTCs 500-503):Vehicle speed sensor diagnostics areperformed for deterioration of magnetic reluctance and electrical characteristics. In case of electricalcircuit malfunction fault code 500 is assigned. If the sensor circuit is indicating out of range reading fault code 501 is assigned. If the sensor circuit isindicating very low reading fault code 502 is assigned. If the sensor is indicating very high/erratic/intermittent reading fault code 503 is assigned.

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Misfire Detector( DTCs 300-312):

Misfire sensor diagnostics areperformed for reduction of cylinder torque due to lack of combustion. In case of detecting misfire in cylinder 1 fault code 300 is assigned. The fault codes for misfires in cylinder 2 to 12 are similarly assigned to 301 - 312respectively. Misfire is described in detail in a later section.

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Evaporative Emission control system (Purge flow) Evaporative Emission control system (Purge flow) (( DTCsDTCs 465465--469):469):Purge flow sensor circuit diagnostics are performed for deteriPurge flow sensor circuit diagnostics are performed for deterioration oration of of Purge flow sensor circuit Purge flow sensor circuit . In case of Purge flow sensor circuit . In case of Purge flow sensor circuit malfunction fault code 465 is assigned. If the Purge flow sensmalfunction fault code 465 is assigned. If the Purge flow sensor or circuit is having range/performance problem purge flow fault cocircuit is having range/performance problem purge flow fault code de 466 is assigned. If the Purge flow sensor circuit has detected 466 is assigned. If the Purge flow sensor circuit has detected a low a low value, fault code 467 is assigned. If the Purge flow sensorvalue, fault code 467 is assigned. If the Purge flow sensor circuit circuit has detected a high value, fault code 468 is assigned. If thehas detected a high value, fault code 468 is assigned. If the Purge Purge flow sensor circuit has intermittent fault, fault code 469 is flow sensor circuit has intermittent fault, fault code 469 is assigned..assigned..

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Evaporative Emission control system (Purge valve) Evaporative Emission control system (Purge valve) (( DTCsDTCs 440440--445):445):Purge valve diagnostics are performed for deterioration of evaPurge valve diagnostics are performed for deterioration of evaporative emission porative emission control system. In case of evaporative emission control system control system. In case of evaporative emission control system malfunction fault malfunction fault code 440 is assigned. If the evaporative emission control systcode 440 is assigned. If the evaporative emission control system is having em is having incorrect purge flow due to faulty purge valve, fault code 441 iincorrect purge flow due to faulty purge valve, fault code 441 is assigned. If the s assigned. If the evaporative emission control system has detected small leak, fevaporative emission control system has detected small leak, fault code 442 is ault code 442 is assigned. If the evaporative emission control system has purge cassigned. If the evaporative emission control system has purge control valve ontrol valve circuit malfunction fault code 443 is assigned. If the evaporcircuit malfunction fault code 443 is assigned. If the evaporative emission control ative emission control system has purge control valve circuit open, fault code 444 issystem has purge control valve circuit open, fault code 444 is assigned. If the assigned. If the evaporative emission control system has purge control valve circevaporative emission control system has purge control valve circuit shorted fault uit shorted fault code 445 is assigned. Evaporative system diagnostics are covecode 445 is assigned. Evaporative system diagnostics are covered in detail in a red in detail in a later section.later section.

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Evaporative Emission control system (Vent valve) Evaporative Emission control system (Vent valve) (( DTCsDTCs 446446--449):449):If the evaporative emission control system vent control circuiIf the evaporative emission control system vent control circuit t malfunction fault code 446 is assigned. malfunction fault code 446 is assigned. If the evaporative emission control system vent control circuit If the evaporative emission control system vent control circuit open, fault code 447 is assigned. open, fault code 447 is assigned. If the evaporative emission control system vent control circuit If the evaporative emission control system vent control circuit shorted, fault code 448 is assigned. shorted, fault code 448 is assigned. If the evaporative emission control system vent valve/solenoidIf the evaporative emission control system vent valve/solenoid circuit circuit malfunction, fault code 449 is assigned. Evaporative emission malfunction, fault code 449 is assigned. Evaporative emission control control system diagnostics are described in detail in later section.system diagnostics are described in detail in later section.

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Evaporative Emission control system (Pressure sensor) Evaporative Emission control system (Pressure sensor) (( DTCsDTCs 450450--455):455):If the evaporative emission control system pressure sensorIf the evaporative emission control system pressure sensoris experiencing malfunction, fault code 450 is assigned. is experiencing malfunction, fault code 450 is assigned. If the evaporative emission control system pressure sensorIf the evaporative emission control system pressure sensorhas range/performance problem, fault code 451 is assigned. has range/performance problem, fault code 451 is assigned. If the evaporative emission control system pressure sensorIf the evaporative emission control system pressure sensorhas low input, fault code 452 is assigned. has low input, fault code 452 is assigned. If the evaporative emission control system pressure sensorIf the evaporative emission control system pressure sensorhas high input, fault code 453 is assigned.has high input, fault code 453 is assigned.If the evaporative emission control system pressure sensorIf the evaporative emission control system pressure sensoris experiencing intermittent fault, fault code 454 is assigned.is experiencing intermittent fault, fault code 454 is assigned.If the evaporative emission control system pressure sensorIf the evaporative emission control system pressure sensoris detected having leak, which is gross, fault code 455 is assis detected having leak, which is gross, fault code 455 is assigned.igned.

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Ignition Coil Ignition Coil (( DTCsDTCs 350350--379):379):Ignition coil diagnostics are performed for deterioration of Ignition coil diagnostics are performed for deterioration of ignition coil ignition coil primary/secondary characteristics. In case of ignition coil primprimary/secondary characteristics. In case of ignition coil primary/secondary electrical ary/secondary electrical circuit malfunction, fault code 350 is assigned. circuit malfunction, fault code 350 is assigned. In case of ignition coil A primary/secondary electrical circuit In case of ignition coil A primary/secondary electrical circuit malfunction, fault code 351 malfunction, fault code 351 is assigned. Similarly for the case of ignition coil B to L priis assigned. Similarly for the case of ignition coil B to L primary/secondary electrical mary/secondary electrical circuit s' malfunction, fault codes 352circuit s' malfunction, fault codes 352--362 are assigned. If timing reference high 362 are assigned. If timing reference high resolution signal A has malfunction fault code 370 is assigned.resolution signal A has malfunction fault code 370 is assigned. If timing reference high If timing reference high resolution signal A has too many pulses fault code 371 is assigresolution signal A has too many pulses fault code 371 is assigned.ned.If timing reference high resolution signal A has too few pulses If timing reference high resolution signal A has too few pulses fault code 372 is assigned. fault code 372 is assigned. If timing reference high resolution signal A has intermittent fIf timing reference high resolution signal A has intermittent fault, fault code 373 is ault, fault code 373 is assigned.assigned.If timing reference high resolution signal A has no pulses, faulIf timing reference high resolution signal A has no pulses, fault code 374 is assigned.t code 374 is assigned.If timing reference high resolution signal B has similar faults,If timing reference high resolution signal B has similar faults, fault codes 375fault codes 375--379 379 respectively are assigned. respectively are assigned.

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Fuel Trim Fuel system (fuel metering) (Fuel Trim Fuel system (fuel metering) ( DTCsDTCs 170170--195, 230195, 230--233 ):233 ):Fuel trim diagnostics are performed for deterioration of fuel Fuel trim diagnostics are performed for deterioration of fuel trim values. trim values. In case of fuel trim malfunction (Bank 1)fault code 170 is assIn case of fuel trim malfunction (Bank 1)fault code 170 is assigned. If the igned. If the fuel trim is indicating too lean system, fault code 171 is assifuel trim is indicating too lean system, fault code 171 is assigned. If the gned. If the fuel trim is indicating too rich system fault code 172 is assifuel trim is indicating too rich system fault code 172 is assigned. gned. In case of fuel trim malfunction (Bank 2)fault code 173 is assIn case of fuel trim malfunction (Bank 2)fault code 173 is assigned. If the igned. If the fuel trim is indicating too lean system, fault code 174 is assifuel trim is indicating too lean system, fault code 174 is assigned. If the gned. If the fuel trim is indicating too rich system fault code 175 is assifuel trim is indicating too rich system fault code 175 is assigned. Fuel gned. Fuel trim diagnostics are described in detail in later section.trim diagnostics are described in detail in later section.

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Individual Fuel Injectors Individual Fuel Injectors (( DTCsDTCs 251251--296):296):Injection pump fuel metering control circuit diagnostics areInjection pump fuel metering control circuit diagnostics areperformed for deterioration of fuel injection characteristics.performed for deterioration of fuel injection characteristics. In case of Injection pump fuel In case of Injection pump fuel

metering control A (Cam/rotor/injector) malfunction, fault codemetering control A (Cam/rotor/injector) malfunction, fault code 251 is assigned. In case of 251 is assigned. In case of Injection pump fuel metering control A (Cam/rotor/injector) rangInjection pump fuel metering control A (Cam/rotor/injector) range/performance problem, e/performance problem, fault code 252 is assigned. In case of Injection pump fuel metefault code 252 is assigned. In case of Injection pump fuel metering control A ring control A (Cam/rotor/injector) Low value, fault code 253 is assigned. In(Cam/rotor/injector) Low value, fault code 253 is assigned. In case of Injection pump fuel case of Injection pump fuel metering control A (Cam/rotor/injector) high value, fault code metering control A (Cam/rotor/injector) high value, fault code 254 is assigned. In case of 254 is assigned. In case of Injection pump fuel metering control A (Cam/rotor/injector) inteInjection pump fuel metering control A (Cam/rotor/injector) intermittent fault, fault code rmittent fault, fault code 255 is assigned. For control “B” 255 is assigned. For control “B” faults similar to “A”, fault codes 256 to 260 are respectively afaults similar to “A”, fault codes 256 to 260 are respectively assigned.ssigned.fault codes 261fault codes 261--296 are assigned to injector coil circuits of cylinders 1 to 12 296 are assigned to injector coil circuits of cylinders 1 to 12 for low value, high for low value, high value, and contribution/balance fault respectively. value, and contribution/balance fault respectively.

EGR EGR Sensor /Valve Sensor /Valve (( DTCsDTCs 400400--408):408):EGR sensor/ valve diagnostics areEGR sensor/ valve diagnostics areperformed for deterioration of exhaust gas flow characteristicperformed for deterioration of exhaust gas flow characteristics. In case s. In case of EGR flow malfunction fault code 400 is assigned. If the EGof EGR flow malfunction fault code 400 is assigned. If the EGR flow is R flow is indicating insufficient flow, fault code 401 is assigned. If thindicating insufficient flow, fault code 401 is assigned. If the EGR flow e EGR flow is indicating excessive flow, fault code 402 is assigned. If is indicating excessive flow, fault code 402 is assigned. If the EGR the EGR circuit malfunction, fault code 403 is assigned. If the EGR cicircuit malfunction, fault code 403 is assigned. If the EGR circuit is rcuit is indicating range/performance problem , fault code 404 is assignindicating range/performance problem , fault code 404 is assigned. ed. If the EGR sensor A circuit is indicating low value, fault cIf the EGR sensor A circuit is indicating low value, fault code 405 is ode 405 is assigned. If the EGR sensor A circuit is indicating high value,assigned. If the EGR sensor A circuit is indicating high value, fault code fault code 406 is assigned. Similar faults on sensor “B” circuit are ass406 is assigned. Similar faults on sensor “B” circuit are assigned fault igned fault codes 407, 408 respectively. EGR sensor/valve diagnostics are codes 407, 408 respectively. EGR sensor/valve diagnostics are described in detail in later section.

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described in detail in later section.

Fundamentals ofFundamentals of PowertrainPowertrainControl strategies & OBD II Control strategies & OBD II DiagnosticsDiagnostics

Idle air control (IAC) valve 505Idle air control (IAC) valve 505--507 507 Idle control system diagnostics areIdle control system diagnostics areperformed for deterioration of idle air flow characteristics. performed for deterioration of idle air flow characteristics. In case of idle air In case of idle air control system malfunction fault code 505 is assigned. If the control system malfunction fault code 505 is assigned. If the idle air control idle air control system is indicating lower than expected flow, fault code 506 isystem is indicating lower than expected flow, fault code 506 is assigned. If s assigned. If the idle air control system is indicating higher than expected fthe idle air control system is indicating higher than expected flow ,fault code low ,fault code 507 is assigned. 507 is assigned.

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Secondary air injection system Secondary air injection system (( DTCsDTCs 410410--419):419):Secondary air injection system diagnostics areSecondary air injection system diagnostics areperformed for deterioration of Secondary air injection system performed for deterioration of Secondary air injection system flow characteristics. In case of flow characteristics. In case of

Secondary air injection system malfunction, fault code 410 is aSecondary air injection system malfunction, fault code 410 is assigned. In case of Secondary air ssigned. In case of Secondary air injection system incorrect flow, fault code 411 is assigned. injection system incorrect flow, fault code 411 is assigned. In case of Secondary air injection In case of Secondary air injection system switching valve A circuit open , fault code 413 is assisystem switching valve A circuit open , fault code 413 is assigned. gned. In case of Secondary air injection system switching valve A circIn case of Secondary air injection system switching valve A circuit shorted , fault code 414 is uit shorted , fault code 414 is assigned. In case of Secondary air injection system switching vaassigned. In case of Secondary air injection system switching valve B circuit malfunction, open , lve B circuit malfunction, open , or shorted, fault codes 415or shorted, fault codes 415--417 are assigned respectively. In case of Secondary air inject417 are assigned respectively. In case of Secondary air injection ion system Relay A circuit malfunction , fault code 418 is assignsystem Relay A circuit malfunction , fault code 418 is assigned. In case of Secondary air ed. In case of Secondary air injection system Relay B circuit malfunction , fault code 419 injection system Relay B circuit malfunction , fault code 419 is assigned. is assigned. Secondary air injection system diagnostics are described in detaSecondary air injection system diagnostics are described in detail in later section.il in later section.

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Fuel level Sensor Fuel level Sensor (( DTCsDTCs 460460--464):464):Fuel level sensor circuit diagnostics are performed for deteriFuel level sensor circuit diagnostics are performed for deterioration of fuel level oration of fuel level sensor characteristics. In case of fuel level sensor sensor characteristics. In case of fuel level sensor circuit malfunction fault code 460 is assigned. If the circuit malfunction fault code 460 is assigned. If the fuel level sensor circuit is indicating out of range/performancefuel level sensor circuit is indicating out of range/performance problem, fault problem, fault code 461 is assigned. If the fuel level sensor circuitcode 461 is assigned. If the fuel level sensor circuitis indicating very low reading, fault code 462 is assigned.is indicating very low reading, fault code 462 is assigned. If the If the fuel level sensor circuit is indicating very high reading faulfuel level sensor circuit is indicating very high reading fault code 463 is assigned. t code 463 is assigned. The expected value is estimated using flow parameters. If the The expected value is estimated using flow parameters. If the fuel level sensor circuit is indicating intermittent faulty fuel level sensor circuit is indicating intermittent faulty reading, fault code 464 is reading, fault code 464 is assigned.assigned.

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Catalytic converter Catalytic converter (( DTCsDTCs 420420--434):434):Catalyst system efficiency diagnostics are performed for Catalyst system efficiency diagnostics are performed for deterioration of characteristics, for Bank 1. In case of Catalydeterioration of characteristics, for Bank 1. In case of Catalyst st system efficiency below threshold, fault code 420 is assigned.system efficiency below threshold, fault code 420 is assigned. In In case of Warm Up Catalyst efficiency below threshold, fault codecase of Warm Up Catalyst efficiency below threshold, fault code421 is assigned. In case of Main Catalyst efficiency below 421 is assigned. In case of Main Catalyst efficiency below threshold, fault code 422 is assigned. In case of Heated Catalythreshold, fault code 422 is assigned. In case of Heated Catalyst st efficiency below threshold, fault code 423 is assigned. In casefficiency below threshold, fault code 423 is assigned. In case of e of Heated catalyst temperature, below threshold, fault code 424 isHeated catalyst temperature, below threshold, fault code 424 isassigned. For identical faults for Bank2 , fault codes 430 to 43assigned. For identical faults for Bank2 , fault codes 430 to 434 4 are respectively assigned. Catalytic converter diagnostics are are respectively assigned. Catalytic converter diagnostics are described in detail in later section.described in detail in later section.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

OBD II tests all sensors, actuators (valves) , switches, and wirOBD II tests all sensors, actuators (valves) , switches, and wiring for proper connectivity, ing for proper connectivity, and checks the inputs and outputs of each device are within alland checks the inputs and outputs of each device are within allowed range of values. The owed range of values. The following sensors and actuators are tested and monitored by the following sensors and actuators are tested and monitored by the OBD II diagnostics:OBD II diagnostics:Coolant temperature sensorCoolant temperature sensorIntake air temperature sensorIntake air temperature sensorManifold Absolute Pressure (MAP) sensorManifold Absolute Pressure (MAP) sensorEngine Speed (Angular speed) sensorEngine Speed (Angular speed) sensorExhaust Gas Oxygen (EGO) sensorExhaust Gas Oxygen (EGO) sensorThrottle Position (Angle) (TPS) sensorThrottle Position (Angle) (TPS) sensorCrankshaft (angular) Position sensorCrankshaft (angular) Position sensorMass Air Flow (MAF) sensorMass Air Flow (MAF) sensorKnock sensorKnock sensorIgnition timing sensorIgnition timing sensorIgnition actuatorIgnition actuatorIdle air control (IAC) valveIdle air control (IAC) valveSecondary air valve Secondary air valve EGR actuator (EGR actuator (pintlepintle valve)valve)Fuel metering actuatorFuel metering actuatorFuel injectorFuel injector

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Each sensor circuit listed below consists of mainly three parts:Each sensor circuit listed below consists of mainly three parts:Sensor, A signal processor, and a display device.Sensor, A signal processor, and a display device.A Sensor converts the physical quantity such as temperature, A Sensor converts the physical quantity such as temperature, pressure, vacuum, RPM,pressure, vacuum, RPM,air flow, velocity, or acceleration into an electrical signal soair flow, velocity, or acceleration into an electrical signal so that that it may be it may be operated by the signal processor operated by the signal processor

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

A signal processor performs some operation on the A signal processor performs some operation on the intermediate signal, to increase power level, reliability, and intermediate signal, to increase power level, reliability, and accuracy. The signal is then manipulated into a form so that accuracy. The signal is then manipulated into a form so that when displayed, it can be understood by the viewer.when displayed, it can be understood by the viewer.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

The display device converts the signal from signal processor The display device converts the signal from signal processor into a readable quantity.into a readable quantity.The sensor converts energy from the form The sensor converts energy from the form of the measurement variable to an electrical signal. An ideal of the measurement variable to an electrical signal. An ideal analog sensor generates an output voltage which is analog sensor generates an output voltage which is proportional to the quantity being measured:proportional to the quantity being measured:vv0 0 = Kq= Kq00, where K is the sensor calibration constant, v, where K is the sensor calibration constant, v00 is is voltage, and qvoltage, and q00 is the measured physical quantity, such as is the measured physical quantity, such as temperature, etc. temperature, etc.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

K is the sensor Calibration constant whose units are volts per K is the sensor Calibration constant whose units are volts per physical quantity measured. An ideal sensor has a linear physical quantity measured. An ideal sensor has a linear transfer characteristic. Real sensortransfer characteristic. Real sensorhas noisy transfer characteristic. As a consequence the sensor has noisy transfer characteristic. As a consequence the sensor output needs signal processing which compensates for the noise output needs signal processing which compensates for the noise and transforms it, suitable for display. and transforms it, suitable for display.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Coolant temperature sensor: Coolant temperature sensor: Principle of operation: The sensor consists of aconsists of athermisterthermister mounted in a housing which is designed to be inserted in the comounted in a housing which is designed to be inserted in the coolant olant stream. This housing is threaded with pipe threads which seal thstream. This housing is threaded with pipe threads which seal the assembly against e assembly against coolant leakage. Acoolant leakage. A thermisterthermister is made of a semiconductor with a negative is made of a semiconductor with a negative temperature coefficient. The sensor is connected in an electrictemperature coefficient. The sensor is connected in an electrical circuit. see Figure al circuit. see Figure in handout. The sensor output varies inversely with temperaturin handout. The sensor output varies inversely with temperature. e.

Diagnostics: The electrical characteristics of the thermister may deteriorate with time. The reference voltage, and the series resister in the circuit are critical sources of variation from correct temperature. The relation between resistance and temperature is not linear in thermister. Silicon temperature sensors provide amore linear output signal and are expected to replace thermister.

OBD II DTCs : There are two failure modes. One is engine coolant temperature not correct, and other is insufficient temperature for closed-loop operation orunstable operation.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Intake air temperature sensorIntake air temperature sensor Principle of operation:

Diagnostics: The electrical characteristics of the thermister may deteriorate with time. The reference voltage, and the series resister in the circuit are critical sources of variation from correct temperature. The relation between resistance and temperature is not linear in thermister. Silicon temperature sensors provide amore linear output signal and are expected to replace thermister.

OBD II DTCs : There is one failure mode. It is intake air temperature not correct. OBD II DTC s are 110-114.

The sensor is similar in construction to the coolant temperature sensor. It is installedin the air intake manifold upstream of the air flow meter. The temperature vsvoltage across the thermister is not completely linear.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics :

Diagnostics

OBD II DTCs

The electrical characteristics of the strain gauge MAP sensor may deteriorate, resulting inincorrect output, stuck at low signal, stuck at high signal,, and intermittent failure.

The failure modes of MAP sensor are diagnosed by OBD II.DTCs for these faults are 105-109.

Manifold Absolute Pressure (MAP) sensor: Manifold Absolute Pressure (MAP) sensor: Principle of operation: The sensor measures the the The sensor measures the the displacement of a diaphragm which is deflected by the manifold adisplacement of a diaphragm which is deflected by the manifold absolute pressure. There are two versions. In bsolute pressure. There are two versions. In strain gauge MAP sensor, the silicon diaphragm is sealed to astrain gauge MAP sensor, the silicon diaphragm is sealed to a pyrexpyrex plate under vacuum. A set of sensing plate under vacuum. A set of sensing resistors is formed around the edge of this vacuum. The resistorresistors is formed around the edge of this vacuum. The resistors are formed by diffusing a “doping s are formed by diffusing a “doping impurity” into the silicon. Manifold pressure applied to the diaimpurity” into the silicon. Manifold pressure applied to the diaphragm cause it to deflect which changes the phragm cause it to deflect which changes the resistance due toresistance due to piezoresistivity piezoresistivity proportional to the pressure. An electrical signal voltage, propproportional to the pressure. An electrical signal voltage, proportional to the manifold pressure is obtained byortional to the manifold pressure is obtained byconnecting the resistors in a Wheatstone bridge. In the second vconnecting the resistors in a Wheatstone bridge. In the second version of MAP sensor, a film electrode ersion of MAP sensor, a film electrode is deposited on the inside face of two alumina plates forming a is deposited on the inside face of two alumina plates forming a capacitor. The capacitor capsule is placed in a capacitor. The capacitor capsule is placed in a sealed housing which is connected to manifold pressure by a smalsealed housing which is connected to manifold pressure by a small diameter tube. The deflection of these l diameter tube. The deflection of these plates when pressure is applied to them , causes their capacitanplates when pressure is applied to them , causes their capacitance to change proportional to the applied ce to change proportional to the applied pressure. The capacitor is placed in an oscillator circuit. the pressure. The capacitor is placed in an oscillator circuit. the frequency of oscillation is proportional to intake frequency of oscillation is proportional to intake temperature. temperature.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Principle of operation

Diagnostics

OBD II DTCs

Engine Speed (Angular speed) sensorEngine Speed (Angular speed) sensor

The sensor consists of a permanent magnet with a coil of wire wound around it.A steel disk with protruding tabs pass between the pole pieces of this magnet.The disk is mounted on the crankshaft. The number of tabs is half the number of cylinders of the engine. The sensor is of magnetic reluctance type so that a voltage is generated with the frequency which is a multiple of revolutionsper minute (RPM) of the crankshaft. By measuring the frequency of this signal voltage the engine RPM is calculated.

The electrical characteristics of the magnetic reluctance sensor may deteriorate, resulting in incorrect output, stuck at low signal, stuck at high signal,, and intermittent failure..

The failure modes of Engine speed sensor are diagnosed by OBD II.DTCs for these faults are 320-323..

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Exhaust Gas Oxygen (EGO) sensorExhaust Gas Oxygen (EGO) sensorThere are two types of EGO sensors, both based on the use of oxiThere are two types of EGO sensors, both based on the use of oxides of materials.des of materials.One usesOne uses ZirconiaZirconia (ZrO(ZrO22), and the other uses titanium oxide (TiO), and the other uses titanium oxide (TiO2 2 ). But ZrO). But ZrO22is most popular and is described here. The sensor consists of Zris most popular and is described here. The sensor consists of ZrOO2 2 sandwichedsandwichedbetween two platinum electrodes. One electrode is exposed to exhbetween two platinum electrodes. One electrode is exposed to exhaust gas aust gas in the exhaust manifold, and the other electrode is exposed to nin the exhaust manifold, and the other electrode is exposed to normal air for ormal air for reference. The electrode that is exposed to exhaust gas is coatereference. The electrode that is exposed to exhaust gas is coated with porous protective d with porous protective overcoat. overcoat. The ZrOThe ZrO2 2 attracts oxygen ions and they accumulate on theattracts oxygen ions and they accumulate on theZrOZrO2 2 surface just inside platinum electrode. AS oxygen ions are negatsurface just inside platinum electrode. AS oxygen ions are negatively ively charged, there will be a potential across the two electrodes if charged, there will be a potential across the two electrodes if the oxygen ionsthe oxygen ionson exhaust gas side are less than the oxygen ions on the normalon exhaust gas side are less than the oxygen ions on the normal air side. The air side. The polarity of this voltage is positive on the exhaust gas side andpolarity of this voltage is positive on the exhaust gas side and negative on air side.negative on air side.The voltage depends on the concentration of the oxygen in the exThe voltage depends on the concentration of the oxygen in the exhaust gas and thehaust gas and theEGO sensor temperature. EGO sensor temperature.

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EGO Oxygen sensor:

Diagnostics: Check for abrupt change in voltage at stoichiometry. Must have rapid changes of output voltage in response to exhaust gas oxygen changes.Must have large difference in sensor output voltage between rich and leanA/F ratio conditions. Must have stable voltage with respect to exhaust temperature.

OBD II DTCs

The failure modes of EGO sensor are diagnosed by OBD II.DTCs for these faults are 400-408..

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II 6141Diagnostics6141Diagnostics

Principle of operation

Diagnostics

OBD II DTCs

Throttle Position (Angle) (TPS) sensorThrottle Position (Angle) (TPS) sensorThe sensor is a rotary potentiometer driven by the shaft of the butterfly valve in the throttle , and a linear potentiometer driven by the connecting rodbetween the accelerator pedal and the throttle. The sensor uses a continuous resistive film manufactured with thick film technique. The material is aceremet or resistive plastic compound. As the throttle butterfly valve rotates the potentiometer voltage varies in proportion to the angle of rotation of throttle.

The electrical characteristics of the Throttle position sensor may deteriorate, resulting in incorrect output, out of range/performance values, stuck atlow signal, stuck at high signal,, and intermittent failure..

The failure modes of throttle sensor are diagnosed by OBD II.DTCs for these faults are 120-124.

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Crankshaft (angular) Position sensorCrankshaft (angular) Position sensorThe crankshaft position sensor is similar in operation to enginThe crankshaft position sensor is similar in operation to engine speede speedsensor.sensor.

Principle of operation

Diagnostics:

OBD II DTCs

The electrical characteristics of the Crankshaft position sensor may deteriorate, resulting in incorrect output, out of range/performance values, stuck atlow signal, stuck at high signal,, and intermittent failure..

The failure modes of crankshaft position sensor are diagnosed by OBD II.DTCs for these faults are 335-344.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Principle of operation:Mass Air Flow (MAF) sensorMass Air Flow (MAF) sensorThe sensor consists of a hot film element (resistor) which is electrically heated to a constant temperature, that is measured by a temperature sensor. This element is incorporated in a whetstone bridge with power supply from the output of an amplifier whose input is the differential voltage, of the bridge resistors, which is balanced when there is no air flow over the hot film at constant temperature. When air flows over the film, the film cools and the resistance of the film element drops, causing bridge unbalance thereby producing an input voltage to the amplifier. The output of the amplifier is connected to the bridge circuit and provides power for the circuit. The amplifier voltage changes the resistance in such a way as to maintain a fixed hot film temperature relative to the inlet temperature.The output voltage of the amplifier is a measure of the additional current required to heat the wire back to its original temperature. The additional current required is a measure of the heat transfer and therefore of air mass flow rate. The second arm of the bridge is a similar self-heated wire, placed in still air which provides compensation for changes in air temperature. and amplifier output voltage. This voltage is converted to frequency which is measured by PCM using a counter. The counter value is proportional to the air flow rate (volume) from which the mass is computed by multiplying the volume by the air density at that temperature.

Diagnostics: The electrical characteristics of the Mass Air Flow sensor may deteriorate, resulting in incorrect output, out of range/performance values, stuck at low signal, stuck at high signal,, and intermittent failure..

OBD II DTCs : The failure modes of crankshaft position sensor are diagnosed by OBD II. DTCs for these faults are 100-104.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Principle of operation

Diagnostics

OBD II DTCs

The sensor measures the sudden rise

The electrical characteristics of the Knock sensor may deteriorate, resulting in incorrect output, out of range/performance values,stuck at low signal, stuck at high signal,, and intermittent failure.

The failure modes of knock sensor are diagnosed by OBD II. DTCs for these faults are 325-329.

Knock sensor Knock sensor in cylinder pressure during combustionin cylinder pressure during combustion which commonly occurswhich commonly occurs with high with high manifold pressure and excessive spark advance. The sensor consimanifold pressure and excessive spark advance. The sensor consists ofsts ofmagnetorestrictivemagnetorestrictive rods placed in a magnetic field of a coil. When excessive cylinrods placed in a magnetic field of a coil. When excessive cylinderderpressure is sensed the rods change the flux field in the coil whpressure is sensed the rods change the flux field in the coil which produces a voltageich produces a voltagechange in the coil. The engine cylinder is mechanically resonantchange in the coil. The engine cylinder is mechanically resonant to the knockto the knockfrequency band, and the output signal is responsive to the firstfrequency band, and the output signal is responsive to the first time derivative of time derivative of acceleration, also called jerk. The output signal of the sensor acceleration, also called jerk. The output signal of the sensor forms a closed loop forms a closed loop system that retards the ignition to reduce the knock detected atsystem that retards the ignition to reduce the knock detected at the cylinders. The the cylinders. The problem of detecting knock is complicated by the presence ofproblem of detecting knock is complicated by the presence ofother vibrations and noise in the engine. other vibrations and noise in the engine. Another version of knock sensor uses piezoelectric crystals, oAnother version of knock sensor uses piezoelectric crystals, or ther the piezoresistancepiezoresistance of of

a doped silicon semiconductor. a doped silicon semiconductor.

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Ignition timing sensor Ignition timing sensor magnetic reluctance sensor can be used to set ignition timing. In the latter type,

Principle of operation Wiegand-effect sensor or

a variable reluctance sensor is mounted on the engine block near a harmonic damper.A harmonic damper is a steel disk-shaped device connected to the crankshaft at the end opposite the flywheel. The damper has a notch cut in its outer surface. As anotch in the rotating damper passes by a variable reluctance sensor, the decrease in magnetic flux generates a voltage pulse in the sensor circuit. This voltage pulse is used to set ignition timing

Diagnostics The electrical characteristics of the Ignition timing sensor may deteriorate, resulting in incorrect output, out of range/performance values, stuck at low signal, stuck at high signal,, and intermittent failure.

OBD II DTCs The failure modes of ignition timing sensor are diagnosed by OBD II. DTCs for these faults are 350-379.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnosticsPrinciple of operationIgnition actuator

The ignition actuator receives its control pulse from an ignition timing sensor. An ignition timing sensor measures the engine angular position to calculate theposition at which the spark should occur. The ignition timing sensor generates a pulse that triggers an electronic circuit that in turn drives the coil primary. This circuit, when so triggered, switches off the current in the coil primary, thereby initiating the spark. The concept of an engine position sensor used as an ignition timing sensor is described previously.In another scheme, a permanent magnet

couples to a ferromagnetic element which mounted on the distributor shaft and rotates with it. As this element rotates , the time varying magnetic field inducesa voltage in the coil that is proportional to the rate of change of magnetic field. Each time one of the cogs on the ferromagnetic wheel passes under the coil axis, one of the sawtooth-shaped pulses is generated. This wheel has one cog foreach cylinder , and the voltage pulses provide a timing pulse for calculating the spark time for the corresponding cylinder.

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DiagnosticsThe electrical characteristics of the Ignition actuator may deteriorate, resulting in incorrect output, out of range/performance values, stuck at low signal, stuck at high signal,, and intermittent failure.

OBD II DTCs The failure modes of ignition actuatorare diagnosed by OBD II. DTCs for these faults are 350-379.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Principle of operation

OBD II DTCs

EGR actuatorEGR actuator The EGR actuator is a vacuum operated

diaphragm valve, with a spring that holds the valve closed if no vacuum is applied.The vacuum that operates the diaphragm is supplied by the intake manifold and is controlled by a solenoid operated valve under control of the PCM. When the solenoid is energized by the PCM the EGR valve is opened by the applied vacuum.When the solenoid is deenergized the the vacuum is cut off from the EGR valve and the spring holds the EGR valve closed. The amount of EGR is controlled by the duty cycle of the pulsed control current that is proportional to the average time ofenergized solenoid. The duty cycle, and the valve opening are properly controlledto ensure exact amount of EGR is provided without adversely affecting emissions.

The duty cycle of the current pulse that energizes the solenoid ,

diagnostics.

The failure modes of EGR flow are diagnosed by OBD II. DTCs for these faults are 400-408.

Diagnostics and the EGR amount are correlated periodically by OBD II

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Idle air control (IAC) valveIdle air control (IAC) valve Principle of operation The valve is an electronicallycontrolled throttle bypass valve which allows air to flow around the throttle plate(which is closed due to low engine RPM and vehicle being stationary) and produces thesame effect as if the throttle is slightly opened. A stepper motor opens the pintle (valve)allowing a limited amount of air to bypass the closed throttle plate. The steppermotor controls the pintle movement accurately thus controlling the amount ofbypass opening into the intake manifold. The duty cycle of the stepper motor is controlled by the PCM which monitors the pintle position and commands thestepper motor to move back the pintle to open the bypass by the calculated amount and move the pintle forward to close the bypass at the end of the duty cycle.

The duty cycle of the stepper motor , and the amount of bypass by thepintle valve are correlated periodically by OBD IIdiagnostics. The initial position and the final position of the pintlevalve are continuously checked.

Diagnostics

OBD II DTCs The failure modes of idle air flow are diagnosed by OBD II. DTCs for these faults are 505-507.

Secondary air valvesSecondary air valves Principle of operation:

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The secondary air is controlled by twosolenoid valves similar to the EGR valve. One valve switches airflow to the exhaustsystem or to outside air cleaner. The other valve switches air flow to the exhaust manifold or to the second chamber of the three-way catalytic converter.The air routing is done by the PCM based on engine coolant temperature, andA/F ratio. During cold start the secondary air goes to exhaust manifold, and during closed loop operation, secondary air goes into catalytic converter. During heavy loads and during severe deceleration, secondary air is directed to air cleaner whereit has no effect on exhaust temperature.

Diagnostics The duty cycle of the current pulse that energizes the solenoid , and the secondary air flow are correlated periodically by OBD IIdiagnostics.

OBD II DTCs The failure modes of secondary air flow are diagnosed by OBD II.DTCs for these faults are 410-419.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnosticsPrinciple of operation

Diagnostics

OBD II DTCs

Fuel metering actuatorFuel metering actuator The actuator used for electroniccontrol of fuel metering is the throttle body fuel injector. The TBFI consists of one or two solenoid-operated fuel injectors that are mounted in a housing on the intakemanifold. The fuel is injected into and atomized by the moving air stream that flowsinto the intake manifold. PCM controls the amount of fuel. Fuel metering actuatordelivers fuel in precise amounts under PCM control. The amount of fuel injected intothe cylinder is determined by the length of time that the injectors are energized which istheir duty cycle. The injection time is synchronous with engine speed and is given by:intake air amount/engine speed x compensation coefficient (correction factor) +voltage-compensated injection time. Fuel trim is used to find the correction factor.Compensation coefficients are dependent on driving conditions such as heavy load, idle, or braking. Asynchronous injection is performed during start-up and acceleration. Fuel injectors are based on multipoint injection in which each each injector is mounted on the intake manifold of its cylinder.

PCM monitors the rate of updating fuel trim and the correction factor to determine if the fuel metering actuator (and injectors ) is functioningproperly

The failure modes of fuel system are diagnosed by OBD II. DTCs for these faults are 170-175.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Fuel injector Fuel injector Principle of operation Individual fuel injectors located

in the intake manifold near the intake valve is the current practice. Each fuel injector is a solenoid activated plunger which is normally closed inhibiting fuel delivery. Whenactivated, the valve opens and a predetermined quantity of fuel is sprayed into theair flowing into the cylinder and mixed with this air. This valve opening is timedrelative to the intake stroke by the PCM controller.The fuel injector consists of a spray nozzle and a solenoid operated plunger. Wheneverthe plunger is lifted from the nozzle, fuel flows at a fixed rate through the nozzle intothe air stream going to the intake manifold. The plunger acts as a fuel injection on-offvalve. The plunger position is controlled by a solenoid and a spring. When no current is applied to the solenoid, the plunger is tightly held against the nozzle by a spring.The plunger is pulled away from the nozzle when the solenoid is activated, causingfuel to flow which is under pressure. The solenoid, plunger, and nozzle act as anelectrically switched valve, which is closed or open, depending on whether the the control current is off or on respectively. The fuel flow rate is regulated by fuel pressure and nozzle geometry. The amount of fuel is proportional to the time the valve is open. The control current that operates the fuel injector is pulsed on and off, and the Air/Fuel ratio is proportional to the duty cycle of the pulse train from the PCMcontroller.

Sensors and Actuators Sensors and Actuators Employed in OBD II Employed in OBD II DiagnosticsDiagnostics

Diagnostics The duty cycle of the current pulse that energizes the solenoid , and the fuel amount are correlated periodically by OBD IIdiagnostics.

OBD II DTCs The failure modes of fuel injector are diagnosed by OBD II. DTCs for these faults

are 251-296.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II DiagnosticsOBD II Diagnostics

PowertrainPowertrain Control Module (PCM) performs the following functions in relatControl Module (PCM) performs the following functions in relation to ion to OBD II Diagnostics: OBD II Diagnostics:

Perform microprocessorPerform microprocessor--based self diagnostics to ensure based self diagnostics to ensure correct operation of the PCM and safe storage of correct operation of the PCM and safe storage of OBD II diagnostic data in memory.OBD II diagnostic data in memory.

Perform OnPerform On--Board diagnostics in real time and alert the Board diagnostics in real time and alert the driver by illuminating MIL in case of a faultdriver by illuminating MIL in case of a fault

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations during openand meet OBD II regulations during open--loop loop operation at startoperation at start--up time.up time.

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations in closedand meet OBD II regulations in closed--loop control loop control during normal operation. during normal operation.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

Perform microprocessorPerform microprocessor--based self diagnostics to ensure correct operation based self diagnostics to ensure correct operation of the PCM and safe storage of OBD II diagnostic data inof the PCM and safe storage of OBD II diagnostic data in memory.memory.

The PCM performs the following self diagnostics:The PCM performs the following self diagnostics:

Verify the checksum of the program memory in ROM with its functVerify the checksum of the program memory in ROM with its function and ion and correct version.correct version.

Perform read and write test of RAM cells for fault free memory Perform read and write test of RAM cells for fault free memory

Perform processor functions in CPU, peripheral devices includingPerform processor functions in CPU, peripheral devices including A/DA/Dconverters, watchdog timers, and registers to verify that the prconverters, watchdog timers, and registers to verify that the processor is ocessor is functioning properly.functioning properly.

Perform checks on stored vehicle data and verify that thePerform checks on stored vehicle data and verify that thedata is not corrupted and is within reasonable limits of vehicldata is not corrupted and is within reasonable limits of vehicle operation. e operation.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

Perform OnPerform On--Board diagnostics in real time and alert the driver by illuminatBoard diagnostics in real time and alert the driver by illuminating ing MIL in case of a fault . MIL in case of a fault . The PCM performs on-board diagnostics in real time

by interspersing diagnostics with vehicle control functions. The diagnostics are classified into priority levels from 1 to 8 or 9. The highest priority level tests are done every 1 millisecond, followed by next priority level tests every 5 milliseconds, 10 milliseconds, 20 milliseconds, 50 milliseconds, 100 milliseconds, 200 milliseconds, 500 milliseconds, and 1 second. The highest priority level tests are those thateffect safety and emissions to a high degree according to OBD II regulations. These include Oxygen sensor (lambda sensor) , and fuel trim checks during closed loop operation of the vehicle. The next priority checks are the interrupttimers, and watchdog timers. The next priority tests are sensors, including EGO sensor, Throttle position sensor, Misfire detection, MAP sensor, Engine RPM sensor, MAF sensor, Crankshaft position sensor, and Engine coolant sensor. The next priority tests are EGR intrusive tests, Catalytic converter's secondary air, and canister purge, fuel level sensor, pedal actuator, and ignition timer. The next priority checks are periodic self tests.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD IIOBD II

The PCM is interrupted by the real time scheduler during the performance of its normal vehicle control functions when the on-board tests are due. At this time thePCM saves its current state of the vehicle and performs the diagnostics. Thistakes about 100 microseconds. Then the PCM returns to its normal vehicle control functions. This repeats for each priority level diagnostics. In this manner the PCM spends about 15- 40% of its time to diagnostics and the rest to perform its normal vehicle control functions. The method of testing each component depends on the electrical characteristics and vehicle functions performed by the device. The PCM maintains the low and high limits for each test parameter, and normal range of values and performance requirements for each component that it tests. The PCM also has adequate hardware test capability to find a short circuit, or open circuit, or the noise level of a signal, including battery, power supply, wiring harness, each sensor, actuator and control unit related to emissions control. The PCM tests each sensor by measuring each test parameter, such as input, or outputand comparing it with the expected value stored in the technical data for the sensor.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

The PCM also compares the signals of the components under test with a combination of information provided by other sensors, to verify the reasonableness of values provided by the components. The noise level and the performance of each signal of the component is checked as well. Actuators are tested similarly to the way the sensors are tested for short circuit, open circuit, and range and performance levels. The test method also includes computing a test output of a sensor using different engine parameters and comparing them for compliance. This is called analytical redundancy. The actuator under certain conditions is intrusively activated and its output is measured to verify against the expected value for proper operation. If discrepancies to the nominal values are diagnosed in any component under test , the information is stored in memory with all the relevant supporting data, such as engine speed, MAP sensor, coolant temperature, and others. This is called “Freeze Frame” since it gives the vehicle’s state at the instant of failure of that component.. Thus defects that appearance or under certain conditions can be diagnosed. If the fault occurs only once during several cycles, it is deleted.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

If the fault persists for two cycles consecutively, it is not erased until the defectis repaired by the technician. In case of an out of range output of a sensor , the PCM substitutes a corresponding reasonable value for that vehicle condition of operation. The PCM also provides clear information to the driver byilluminating the MIL (Malfunction Indicator Light) in case of a defect without causing alarm for minor problems. All relevant data for off-board diagnostics, and repair are stored by the PCM in its memory for later use. In the case of a defect that completely impairs the vehicle performance the PCM has the fullcapability to switch the vehicle state to a safe state of lesser capability called “Limp Home” state, in which the vehicle is brought to a safe degraded operating condition, that includes a halt of the vehicle. The PCM communicates with the OBD II scan tool and provides diagnostic data, and OBD II DTCs of all faultsexperienced by the vehicle so far to the external tester to facilitate off-board diagnostics, and vehicle repair. In this respect OBD II provides SAE J 1850 datalink for communication of diagnostic data, SAE J 2012 provides the DTC messageformats, and SAE J 1979 provides the test modes, requesting PCM for emissionsrelated powertrain diagnostics data.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

OBD II Functions: These include catalyst monitoring, misfire monitoring, evaporative system monitoring, secondary air system monitoring, fuel systemmonitoring, oxygen sensor, monitoring, EGR (exhaust gas recirculation) systemmonitoring, and comprehensive component monitoring.Catalyst: PCM shall individually monitor the front catalyst or catalysts which receive untreated engine out exhaust gas for malfunction. This is done by monitoring the oxygen sensor in front of the catalyst. In addition the PCMshall monitor the oxygen sensor situated down stream of the catalyst, and comparethe signals of the two sensors to verify that the catalysts are functioning properly.A properly functioning catalyst shows a storage effect such that the oscillationsof the lambda oxygen sensor at the down stream of the catalyst are minimal orzero, while the upstream oxygen sensor is oscillating with amplitude and frequency of the limit cycle of the rich/lean, air /fuel mixture.Misfire Detection: The PCM shall monitor engine misfire and identify cylinderexperiencing misfire. If a certain percentage of misfires within 200 or 1000 revolutionsis detected, a fault code is stored by the PCM and the MIL is illuminated by the PCM.Misfire detection is critical to emissions and is described in detail in a later section.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

Oxygen sensor: The PCM shall monitor the output voltage, the response rate, and other parameters that can affect emissions, and all fuel control oxygen sensors for malfunction. The algorithm involves monitoring for short circuit, or breaks, and monitoring the switching frequency of the closed-loop control. If this is too slow or too fast relative to the limit cycle frequency of the air/fuel mixture, then theoxygen sensor is deemed defective. The PCM illuminates the MIL in the event of a fault and stores the DTC and diagnostic data in memory. Heated sensors are monitored using heater current, voltage, and sensor temperature .Evaporative system: The PCM shall control the air flow of the complete evaporativesystem. The PCM shall also monitor the emission of HC vapors into the atmosphereby performing a pressure check and a vacuum check of the purge valve, and the canister valve, using intrusive purge operations. The algorithm is two fold. At idle position, the purge valve is activated and the lambda sensor is monitoredfor its reaction which should indicate a rich reading (high voltage of 900 mv). For leak detection of the evaporative system, the canister valve is closed, and the canister pressure is decreased to about about -1.5 KPa. Then the complete system is turned off and the pressurewithin the canister is monitored for variation with time. The pressure gradient, together with other parameters like the amount of fuel, may indicate a leak. If the leak persists for twoconsecutive cycles, the MIL is illuminated.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

Secondary Air system: The PCM shall monitor the secondary air delivery systemand proper functioning of the air switching valves. The algorithm consists in monitoring the lambda sensor for correlated deviations when the secondary air flow is changed from exhaust manifold or to catalyst chamber or to outside air cleaner.Fuel system: The PCM shall monitor the fuel delivery system. The algorithm is to monitor the deviations of the stoichiometric ratio which last for a longer time and store them within the adaptive mixture controller consisting of short term fuel trim, and long term block learn. If these values exceed defined limits, components of the fuel system are deemed defective. This will result in illuminating the MIL and storing the DTC in memory.Exhaust Gas Recirculation (EGR) system: The PCM shall monitor the EGR system for low and high flow rate malfunctions. The algorithm is two fold: At overrun, the fuel is cut off and the EGR valve is completely opened. The flow of exhaust gas to the intake manifold raises the manifold pressure, which is recorded. Secondly monitor the increase of he manifold intake temperature when the EGR valve is opened.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations during openand meet OBD II regulations during open--loop operation at startloop operation at start--up time.up time.

The primary function of the PCM is to control the powertrain operation during the start up and during the warm up conditions. In both the conditions, theprimary function of the PCM is to maintain the Air/Fuel ratio at or nearstoichiometry. The modes in which this control is accomplished are :open-loop control and closed-loop control corresponding to start up and warm up condition respectively. In this section, we consider the open-loop control and in the next section we will describe the closed-loop control by the PCM. The open-loop control by the PCM is in effect during the start up of the vehiclewhen the electronic fuel control system is not controlled by the lambda oxygen sensor due to its low temperature (below 300 C). During this mode thePCM controls the fuel system to remain in stoichiometry by using MAP, Engine RPM, EGR and Coolant temperature sensor in stead of the lambda oxygen sensor.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

The PCM obtains the mass air flow from the MAF sensor and obtains the massfuel required to keep the air/fuel ratio equal to stoichiometry (14.7) from lookup tables. The inputs to the lookup table is MAP, Engine RPM, Coolant temperature,and EGR, all of which are readily available by computation, or lookup table.The value of the speed density product Ra* da is given by:

Ra = (Engine RPM/60) * ( Engine displacement/2)* volumetric efficiency - EGR volume flow rate

da = Ma / Ra , where Ma is the mass of air, and Ra is the volume at in take air temperature T.

Tables of da, the density of air measured versus temperature are available in lookup tables.Engine displacement and volumetric efficiency are engine design parameters, which areconstant. Lookup tables with inputs: Engine RPM, MAP, T, and EGR give directly the mass flow rate of air, which is product Ra* da . This is used as input into another lookup table that gives the duty cycle of the fuel injector, which gives the amount of fuel required to keep the A/F mixture at stoichiometry. This lookup is performed by the PCM to complywith OBD II regulation mandated by CARB and EPA for controlling emissions..

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations in closedand meet OBD II regulations in closed--loop control loop control during normal operation.during normal operation.

Closed-loop mode of control is selected by PCM when the lambda sensor has attained a temperature more than 3000 C. The intake Air/Fuel ratio is controlled in a closed loop by measuring the EGO at the exhaust manifold and altering the input fuel flow rate with fuel injector to correct for a rich orlean mixture indication. The PCM continuously adjusts the output signal to the fuel injector to maintain stoichiometry by varying the duty cycle. Variationsin engine transport delay with RPM are corrected by reducing the cycle frequency and duty cycle ramp rate with decreasing RPM. The fuel flow is corrected by using fuel trim correction using short term update and long term update scheme, to compensate for the engine performance over time.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations in closedand meet OBD II regulations in closed--loop control. loop control.

Acceleration Enrichment: When heavy load is demanded by the driver, thePCM adjusts the fuel control to provide enriched air/fuel mixture to maximize engine torque and neglect emission control. This is for short time and isapproved by EPA. The PCM performs this by detecting high throttling anglesensor voltage or high MAP sensor value. In case WOT, the PCM increases the duty cycle of the fuel injector to the maximum allowed value, which may result in A/F ratio of as low as 12:1.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations.and meet OBD II regulations.

Deceleration Enleanment and Idle Speed Control: When the driver decelerates the vehicle very hard, the PCM reduces the engine torque by cutting off fuel , with decel fuel cut off mode in which the fuel injector is turned off or the duty cycle is drastically reduced. A typical algorithm for fuel injection duration for the desired Air/Fuel ratio of stoichiometry is given by:T = base pulse width from lookup table for mass air flow + closed loop correction factor closed loop correction factor is the fuel trim block learn value alluded earlier.For open-loop control , closed-loop correction factor is zero.For closed-loop operation, correction factor, C, is given by:

C = I*A + B*F, where A and B are constants, and I is the integral part, and F is the fractional part of the correction factor..

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II OBD II

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations.and meet OBD II regulations.

I and F are determined from the fuel trim, and EGO sensor. When EGO indicates rich mixture , Fuel trim value I is reduced by 1, and increased by 1 for lean mixture.The base pulse width of fuel injector is proportional to mass air flow given by:

T = K* Ra , where factor K is determined by the PCM, depending on the Mode offuel control. For closed-loop normal operation, K corresponds to stoichiometric Air/Fuel mixture. For cold start, K corresponds to A/F = 12:1. For deceleration, K=0.The mass air flow is calculated by the PCM as described before.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II DiagnosticsOBD II Diagnostics

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations.and meet OBD II regulations.

Idle Speed Control: When the throttle angle reaches its closed positionand engine RPM falls below a preset value (about 600), the PCM switches to idle speed control mode. The PCM controls the idle air controlpintle (valve) to let air to flow into intake manifold, bypassing the closedthrottle to prevent the engine from stalling due to lack of torque. Thepintle is operated by a stepper motor, which withdraws the pintle from itsclosed position (seat) to open the bypass that lets a limited amount of air flow into the intake manifold. Idle speed is detected by the RPM sensorindicating a low value, the vehicle is stationary, and throttle is closed. ThePCM adjusts the pintle to keep the idle speed around 600 to 700 RPM. Thepintle valve is completely closed when engine is not idling.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II DiagnosticsOBD II Diagnostics

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations in closedand meet OBD II regulations in closed--loop control.loop control.

EGR Control: At high engine load (high throttle angle), and high Engine RPM, and at high engine coolant temperature, the cylinder temperature at combustionreaches temperature greater than 30000 F which causes NOx emissions to increasebeyond the OBD II limits. For this reason, the PCM recirculates a small portion ofthe exhaust gases into the intake manifold. This has the effect of reducing oxygen content without reducing the mass of gas processed. The combustion impartsenergy to the inert exhausts gas as well as to the air charge. The net effect isto retain much of the engine power while reducing the flame temperatureat part load, thus decreasing production of NOx. The PCM controls the EGRvalve depending on the throttle angle, engine RPM, coolant temperature. EGR is completely closed during cold start and during start up of the engine.The duty cycle of the EGR valve is obtained from predefined table lookup.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II DiagnosticsOBD II Diagnostics

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations in closedand meet OBD II regulations in closed--loop control.loop control.

EGR Control (contd) : The EGR signal can either control a valve opening, which is detected by a valve position sensor, or the PCM can meter the exhaust gasin the same way as the PCM meters the fuel in the fuel injector. The PCM uses the sensor similar to throttle position sensor to determine the amount of EGR fed into the air intake during open loop control mode, to make air/fuel ratiocalculation, when it is not stoichiometric ratio. This sensor gives an electrical signal which is proportional to the amount of opening of the EGR valve that can be used to compute the amount of EGR from the knowledge of the valve’s duty cycle.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II DiagnosticsOBD II Diagnostics

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations.and meet OBD II regulations.

Secondary Air management: The PCM controls the powertrain operation inengine warm-up mode by selecting a warm-up time from a table lookuptable based on the coolant temperature. During engine warm-up the Air/Fuelratio is still rich as in during engine crank, when the engine is still cold. The PCMcontrols the powertrain functions in open-loop mode and uses secondary air management to bring up the converter temperature as well as EGO sensor temperature, to go into closed-loop mode as soon as possible when the emissions are lowest and meet OBD II requirements. The PCM provides extra oxygen rich air to either the converter itself, or to the exhaust manifold. The catalyst temperaturemust be above 2000 C to efficiently oxidize HC and CO and reduce NOx to N2 .During warm-up when the catalytic converter is cold, the HC , and CO are oxidized in the exhaust manifold. This creates extra heat to speed warm-up of the converter,and EGO sensor, enabling the PCM to go into closed-loop control.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II DiagnosticsOBD II Diagnostics

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations.and meet OBD II regulations.

Secondary Air management (contd): The converter can be damaged if too much heat is applied to it. This can occur if large amounts of HC and CO are oxidized inexhaust manifold during heavy loads which call for fuel enrichment or during severe deceleration. In such cases, the PCM directs the secondary air to the aircleaner where it has no effect on exhaust temperature.

After warm-up, the main use of secondary air is to provide an oxygen rich air to thesecond chamber of the three-way catalyst, dual-chamber converter system. In the dual chamber converter, the first chamber contains rhodium, and platinum to reduce NOx and to oxidize HC and CO. The second chamber contains only platinumand palladium.. The extra oxygen from the secondary air improves the ability of theconverter to oxidize the HC and CO in the second converter chamber. The PCM controls the secondary air using two solenoid valves similar to EGR valve.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II DiagnosticsOBD II Diagnostics

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations.and meet OBD II regulations.

Secondary Air management (contd): The first solenoid valve switches air flow to theair cleaner or to the exhaust system. The second solenoid valve switches air flow either to the exhaust manifold or to the catalytic converter. The PCM controls the air flow depending on the engine coolant temperature, and Air/Fuel ratio which is notstoichiometric ratio in this mode, which is open-loop control.

Evaporative Emission Canister Purge: The PCM releases the collected fuel fuel vapors in the canister into the intake manifold via a solenoid controlled purge valve periodically, during closed loop operation. This will simplify fuel calculationduring open-loop control.

Functionality ofFunctionality of PowertrainPowertrainControl Module (PCM) in Control Module (PCM) in OBD II DiagnosticsOBD II Diagnostics

PerformPerform powertrainpowertrain control functions to reduce emissions control functions to reduce emissions and meet OBD II regulations.and meet OBD II regulations.

Automatic system Adjustment:: The PCM during closed-loop mode of controlchecks the open-loop calculated air/fuel ratios and compares them with closed-loop average limit values which are the ideal values for minimumemissions. If the difference is large, the PCM corrects the open-loop lookup table values so that the open-loop values are in close agreement with the closed-loop values. This updated open-loop lookup table is stored innon-volatile RAM memory. When the engine is started next time the PCMuses the new lookup values which are closer to the stoichiometric ratio. This feature is important since it enables the PCM to adjust to long-term changes in engine and fuel system conditions due to wear and usage. This is similarto fuel trim algorithm for fuel injection control. These are all the PCM control functions performed to reduce emissions and comply with OBD II requirements.